.  GIFT   OF 

MICHAEL  REESE 


MODERN 
GASWORKS  PRACTICE 


BY 

ALWYNE    MEADE,   Assoc.M.lNST.C.E. 

it 

LECTURER     IN     GAS     ENGINEERING    AND    ALLIED    SUBJECTS    TO    THE    LONDON     COUNTY    COUNCIL 

AND     AT     THE     REGENT     STREET     POLYTECHNIC  ;      MANAGER     OF      THE      WAPPING 

WORKS    OF    THE    COMMERCIAL    GAS    COMPANY;     MILLER    PRIZEMAN    OF 

THE      INSTITUTION     OF     CIVIL     ENGINEERS,      igiO-II, 

ETC.,     ETC 

WITH    AN    INTRODUCTORY  NOTE 

KY 

STANLEY    H.    JONES,  M.INST.C.E.,  ETC. 

ENGINEER    AND   GENERAL    MANAGER   OF    THE   COMMERCIAL   GAS   COMPANY. 


NEW    YORK 

D.    VAN    NOSTRAND    COMPANY 

TWENTY-FIVE  PARK  PLACE. 
LONDON,   OFFICES  OF  "THE  GAS  WORLD." 

1916. 


INTRODUCTORY    NOTE 

THE  Author  has  paid  me  the  compliment  of  asking  me  to  write  an  introductory  note 
to  his  book  MODERN  GASWORKS  PRACTICE,  and  it  affords  me  peculiar  pleasure  to  do 
so,  for  I  have  known  him  throughout  his  professional  career.  He  has  thrown  himself 
into  his  subject  with  characteristic  thoroughness,  dealing  with  the  works  side  of  gas 
engineering  from  alpha  to  omega,  and  his  treatise  will  be,  I  venture  to  think,  a  most 
useful  addition  to  the  bookshelves  of  present-day  gas  engineers. 

The  Author's  literary  work  is  a  fitting  sequel  to  his  technical  ability  and  skill  as 
known  to  and  appreciated  by  one  who  has  had  the  fullest  opportunity  of  judging — 
'  ctvSpa   fiet^ei. 

STANLEY  H.  JONES. 
COMMERCIAL  GASWORKS,  STEPNEY,  E. 
November,  1916. 


376134 


PREFACE 

THE  gas  industry  in  this  country,  in  spite  of  its  magnitude,  is  particularly  ill  fur- 
nished with  anything  in  the  nature  of  a  general  work  of  reference  dealing  with  really 
modern  practice.  The  deficiency,  however,  can  be  readily  understood  when  con- 
sideration is  given  to  the  immensity  of  the  task  with  which  the  intending  author 
is  faced,  the  sacrifice  of  time  involved,  and,  above  all,  the  difficulty  of  keeping  pace 
with  principles  and  ideas  which  are  in  a  perpetual  state  of  development.  Such  pros- 
pects, in  fact,  may  well  be  calculated  to  damp  the  enthusiasm  of  the  most  deter- 
mined aspirant. 

The  author  entered  with  a  light  heart  upon  the  task  of  endeavouring  to  remedy 
the  deficiency,  but  after  twelve  months  of  continuous  work,  with  no  prospect  of 
the  end  in  view,  "  a  change  came  o'er  the  spirit  of  my  dream,"  for  the  enormity  of 
the  subject  was  such  that  there  seemed  little  hope  of  ever  winning  through.  How- 
ever a  plunge  into  the  struggle  for  another  few  months  brought  matters  to  a  con- 
clusion, and  the  present  volume,  whatever  its  merits  or  shortcomings,  is  put  for- 
ward in  the  hope  that  it  may  prove  of  some  assistance  and,  perhaps,  enjoyment  to- 
the  highly  trained  gas  engineer  of  to-day.  It  must  be  realized  at  the  outset  that 
so  far  as  the  principles  and  practice  of  modern  gasmaking  are  concerned  no  single 
individual  can  lay  claim  to  omniscience,  and  on  no  account  would  the  author  pre- 
sume to  be  especially  fitted  for  the  task  he  has  undertaken.  No  pains  have,  how- 
ever, been  spared  to  develop  the  book  essentially  on  the  ideas  of  the  practical  man, 
whilst  every  precaution  has  been  taken  to  avoid  inaccuracies.  In  the  latter  connec- 
tion the  author  has  taken  advantage  (perhaps,  at  so  busy  a  time,  too  much  advan- 
tage) of  the  help  of  his  many  friends  in  the  industry,  with  the  result  that  nearly 
every  chapter  has  been  submitted  for  suggestions  to  an  expert  in  the  particular 
branch  with  which  it  deals.  This  assistance,  involving  as  it  has  in  many  cases  some 
considerable  labour,  has  been  most  generously  given,  and  acknowledgment  to  the  full 
is  due  to  the  following  gentlemen  for  their  services  : — 

Mr.  G.  F.  Handel  Beard,  Mr.  F.  J.  Bradfield,  Mr.  A.  F.  Browne,  Mr.  F.  J.  Bywater, 
Professor  J.  W.  Cobb;  Dr.  H.  G.  Colman,  Mr.  E.  V.  Evans,  Mr.  G.  M.  Gill,  Mr.  Thos. 
Glover,  Mr.  W.  R.  Herring,  Mr.  Charles  Hunt,  Mr.  Frank  H.  Jones,  Dr.  R. 
Lessing,  the  late  Professor  Lewes,  Mr.  R.  J.  Milbourne,  Mr.  Jas.  Stelfox,  Mr.  J.  W. 
Scott,  Mr.  B.  B.  Waller,  Mr.  P.  E.  Williams,  and  Mr.  Henry  Woodall. 

In  addition,  my  thanks  are  due  to  Mr.  Geo.  Evetts,  Assoc.M.Inst.C.E.,  who  has 
read  through  a  large  portion  of  my  manuscript,  and  from  whom  I  have  received  many 
valuable  suggestions.  Mr.  W.  F.  Brown  voluntarily  took  upon  himself  the  task  of 
reading  through  the  volume  in  its  entirety,  checking  all  figures,  chemical  equations, 

vii  b 


viii  PREFACE 

etc.,  with  the  utmost  diligence  and  with  great  help  to  myself.  Needless  to  say>  the 
author  is  nothing  without  his  publishers,  and  it  is  not  possible  to  speak  too  gener- 
ously of  the  assistance  I  have  received  from  this  direction,  or  to  express  my  gratitude 
too  fully  for  the  enterprising  manner  in  which  my  volume  has  been  put  together.  I 
am  indebted  to  the  editors  of  the  Gas  World,  the  Journal  of  Gas  Lighting,  and 
other  technical  papers,  for  permission  to  make  use  of  the  material  contained  in 
various  articles  I  have  written  for  them. 

Finally,  I  have  the  gratification  of  being  able  to  preface  my  book  with  a  forenote 
written  by  Mr.  Stanley  H.  Jones,  M.Inst.C.E.,  chief  engineer  and  general  manager  to 
the  Commercial  Gas  Company.  In  acknowledging  this  support  it  may  not  be  out 
of  place  to  record  the  fact  that  the  whole  of  my  training  in  the  profession  was  carried 
out  under  his  supervision.  Consequently,  the  principles  instilled  into  my  mind  are 
largely  those  of  the  Commercial  Gas  Company,  principles  which,  judging  from 
results  the  world  over,  are  not  to  be  despised. 

A.  M. 

WAPPING  WORKS,  LONDON,  E. 
November,  1916. 


CONTENTS 

PAGE 

INTRODUCTION           ........  1 

CHAP  re  R  I. — THE  PLANNING  AND  LAYING  OUT  OP  GASWORKS     .         .         .  4 
-CHAPTER  II.— FOUNDATIONS,  GASWORKS'  BUILDINGS,  ETC.  .         .         .         .30 

CHAPTER  III. — THE  HORIZONTAL  RETORT  BENCH 46 

CHAPTER  IV. — THE  CONTROL  OF  HORIZONTAL  RETORT  SETTINGS          .         .  83 

CHAPTER  V. — VERTICAL  RETORTS  AND  CHAMBER  OVENS     ....  100 

CHAPTER  VI. — REFRACTORY  MATERIALS     .         .         .         .         .         .         .130 

CHAPTER  VII. — RETORT-BENCH  APPURTENANCES        .         .         .                  .  156 

CHAPTER  VIII. — THE  MECHANICAL  HANDLING  OF  MATERIALS      .         .         .  182 

CHAPTER  IX. — ELECTRICAL  PLANT  IN  GASWORKS        .         .         .         .         .  227 

CHAPTER  X. — GAS-MAKING  AND  OTHER  COALS  .         .         .         .         .         .  233 

CHAPTER  XI. — THE  CARBONIZATION  OF  COAL     .         .         .         .         .^  ,:f,  253 

CHAPTER  XII.— THE  CONDENSATION  OF  COAL  GAS     .         .         .         .         .286 

CHAPTER  XIII. — EXHAUSTING  MACHINERY 305 

CHAPTER  XIV. — THE  PRELIMINARY  PURIFICATION  OF  COAL  GAS          .         .  326 

CHAPTER  XV. — THE  RECOVERY  OF  CYANOGEN  .         .         .         '.  :    .'-/»         .  367 

CHAPTER  XVI.— THE  DRY  PURIFICATION  OF  COAL  GAS      .         .         .         .  383 

CHAPTER  XVII.— THE  STORAGE  OF  GAS 420 

CHAPTER  XVIII. — WATER  GAS  :  ITS  MANUFACTURE,  ENRICHMENT,  AND  USE  466 

INDEX   .  513 


IX 


MODERN    GASWORKS    PRACTICE 


INTRODUCTION 

THE  modern  gas  engineer,  beyond  realizing  that  William  Murdoch  was  the  first 
individual  to  turn  coal  gas  to  some  practical  use,  has  in  many  cases  a  somewhat 
restricted  knowledge  of  the  general  historical  facts  connected  with  the  inception 
and  development  of  the  immense  industry  to  which  he  belongs.  Perhaps,  how- 
ever, this  is  not  surprising  when  consideration  is  taken  of  the  multifarious  duties 
and  accomplishments  now  demanded  of  such  toil-worn  officials,  who,  in  order  to 
excel,  must  combine  the  qualities  of  engineer,  scientist,  and  administrator,  in  addi- 
tion to  possessing  a  specialized  knowledge  of  their  primary  subject.  Under  the 
circumstances  it  has  been  thought  advisable  to  trace  out  briefly  the  more  important 
links  connecting  the  discovery  of  destructive  distillation  with  the  orderly  scientific 
procedure  known  to  us  to-day,  in  the  hope  that  the  reader  with  a  taste  for  historical 
incident  may  find  this  volume  of  some  small  interest  and  assistance. 

The  word  "  Gas  "  is  of  somewhat  uncertain  origin,  but  in  all  probability  it  is 
derived  from  the  Dutch  "  geist,"  meaning  "  spirit,"  although  some  etymologists 
state  good  reasons  for  supposing  that  the  term  was  initially  connected  with  "  chaos." 
The  existence  of  "  fire-damp,"  which  is  more  or  less  closely  allied  to  coal  gas,  appears 
to  have  been  discovered  at  a  comparatively  early  date,  for  Thomas  Shirley  in 
1667  published  an  extended  account  of  his  researches  in  connection  with  a  burning 
spring  near  Wigan.  After  this  there  were  many  similar  observations  of  the  pro- 
duction of  gas  by  the  decomposition  of  vegetable  matter ;  but  credit  for  the  dis- 
covery of  destructive  distillation  most  probably  lies  between  the  famous  Boyle 
and  the  Rev.  John  Clayton,  who  corresponded  in  the  neighbourhood  of  the  year 
1690  en  the  existence  of  this  phenomenon.  It  was  not,  however,  until  nearly  a 
hundred  years  after  this  that  serious  thought  was  given  to  the  possibility  of  utilizing 
gas  as  an  illuminant.  Who  was  the  actual  originator  of  the  idea  is  still  a  matter 
for  dispute,  for  several  persons  seem  to  have  independently  conceived  the  notion 
at  the  same  time.  There  was  the  Belgian,  Minckelers ;  the  Frenchman,  Phillippe 
Lebon ;  and,  in  this  country,  Lord  Dundonald  and  Murdoch ;  but  entire  credit  is 
usually  given  to  the  last-named,  who  commenced  experiments  at  Redruth,  in  Corn- 
wall, in  1792.  In  the  same  year  he  distilled  a  variety  of  carbonaceous  substances, 
including  coal,  wood,  and  peat,  and  made  calculations  comparing  the  cost  of  light 

1  B 


2  INTRODUCTION 

so  obtained  with  that  given  by  the  prevailing  illuminants  at  that  time,  namely 
oil  and  tallow.  Five  years  later  he  lighted  his  own  premises  at  Old  Cumnock,  Ayr- 
shire ;  whilst  in  1802,  in  celebration  of  the  Peace  of  Amiens,  he  arranged  for  the 
brilliant  illumination  of  the  Soho  Works  of  Boulton  &  Watt,  which  firm  he  had 
joined. 

Attention  must  now  be  turned  from  Murdoch  to  a  man  named  Winsor,  who 
was  attracted  by  the  striking  experiments  which  Lebon  was  conducting  in  Paris. 
Winsor  crossed  over  to  France,  endeavoured  to  strike  a  bargain  with  Lebon,  but 
failed,  and  finally  returned  to  England  with  a  full  determination  to  fathom  the  why 
and  wherefore  of  the  whole  business.  He  studied  the  subject,  mastered  it  more 
or  less  imperfectly,  and  exploited  his  invention  in  Germany.  Subsequently  he  re- 
turned to  London,  and  in  1804  gave  a  series  of  lectures  and  exhibitions  at  the  Lyceum 
Theatre,  incidentally  raising  nearly  £50,CCO  for  carrying  out  his  projects.  In  1809, 
he  lighted  a  portion  of  Pall  Mall  with  gas,  this  being  the  first  street  so  dealt  with. 
From  then  onwards  the  reputation  of  the  new  illuminant  was  assured,  although 
undertakings  existing  for  its  manufacture  and  distribution  had  many  uphill  fights 
before  being  established  on  the  road  to  success.  In  the  same  year  Murdoch  and 
Winsor  came  into  collision,  which  resulted  in  the  enterprising  plans  of  the  latter 
being  held  in  abeyance  for  a  time ;  but  1813  saw  the  inauguration  of  the  London 
and  Westminster  Gas  Light  and  Coke  Company,  which  two  years  later  possessed 
three  manufacturing  stations  and  fifteen  miles  of  street  mains.  The  business  of 
supplying  gas  progressed  with  such  rapidity  that  by  1830  more  than  200  companies 
existed  throughout  the  kingdom.  Westminster  Bridge  was  first  lighted  with  gas 
in  December  1813,  and  in  the  following  year  the  parish  of  St.  Margaret,  Westminster. 
As  was  only  to  be  expected,  the  misgivings  of  the  public  were  at  first  difficult  to 
quell,  whilst  profits  were  non-existent,  and  the  outlook  for  the  future  extremely 
questionable.  Soon  afterwards  the  company  dispensed  with  the  services  of  Winsor, 
who,  it  is  recorded,  after  his  dismissal  passed  to  "  the  blackness  of  the  tomb  in  the 
cemetery  of  Pere  la  Chaise,  at  the  age  of  sixty-seven  years." 

The  history  of  gas-lighting  for  the  next  few  years  is  largely  the  history  of  this 
original  company,  the  now  famous  Gas  Light  &  Coke  Company.  The  pioneer  Clegg 
(who  had  left  the  service  of  the  Company  on  a  question  of  salary)  invented  the  gas- 
meter  in  1815,  although  it  was  not  turned  to  any  extensive  practical  use  until  ten 
years  later.  Meanwhile,  the  influence  of  competition  was  beginning  to  make  itself 
felt,  and  it  would  seem  that  there  was  some  occasion  for  it  when  it  is  remembered 
that  the  price  of  gas  at  this  time  was  15s.  pet  1,000  cubic  feet.  About  1820  the  possi- 
bilities of  oil  gas  began  to  be  recognized,  and  a  stout  and  costly  resistance  was  put 
up  by  the  London  companies  to  a  Bill  for  the  promotion  of  an  oil-gas  concern.  The 
Bill  was  ultimately  defeated,  but  in  1823  Bristol  was  lit  by  this  product  under  a 
special  Act.  In  the  same  year  Sir  William  Congreve  (the  Home  Office  inspector  of 
metropolitan  gasworks)  issued  a  report  showing  that  the  annual  production  of 
gas  from  the  three  works  of  the  Gas  Light  &  Coke  Company  was  248  million 
cubic  feet,  whilst  they  possessed  122  miles  of  street  mains.  As  years  went  on  a 
bitter  rivalry  sprang  up  between  the  various  manufacturing  concerns,  and  serious 


INTRODUCTION  3 

consideration  was  given  to  a  scheme  for  the  amalgamation  of  interests.  At  first 
nothing  came  of  this,  but  that  things  were  taking  a  turn  for  the  better  is  indicated 
by  the  fact  that  in  1855  the  premier  company  was  enabled  to  make  a  distribution 
of  6  per  cent.  At  one  time  there  were  no  fewer  than  thirteen  companies  supplying 
London,  but  amalgamation  proceeded  apace,  and  to-day  the  enormous  require- 
ments of  the  metropolis  are  in  the  hands  of  merely  three  companies.  The  year 
1850  witnessed  the  introduction  by  Sir  William  Perkin  of  the  great  aniline  industry 
— since,  unhappily,  almost  entirely  lost  to  Germany ;  and  in  1860  the  Metropolis 
Gas  Act  came  into  force. 

From  then  onwards  the  innumerable  concerns  which  had  sprung  up  in  London 
and  the  provinces  trudged  along  in  a  more  or  less  lethargic  manner  to  the  accom- 
paniment of  increasing  profits  and  abundant  dividends.  There  came,  however, 
a  rude  awakening  in  1883,  when  the  possibilities  of  electric  light  were  first  realized. 
Shareholders  parted  with  their  holdings  in  apprehension,  and  the'  quoted  prices  of 
gas  stock  dropped  materially ;  but  far-seeing  individuals  took  the  opportunity  for 
increasing  their  holdings,  and  soon  had  cause  to  be  gratified  at  their  wisdom. 
As  it  happened,  the  coming  of  electricity  inspired  the  renaissance  of  the  gas  industry. 
Seeing  that  the  uses  of  gas  for  lighting  were  likely  to  undergo  restriction,  engineers 
turned  their  attention  to  other  means  of  disposal ;  and  the  perfection  to  which 
countless  appliances  have  been  brought  to-day  is  in  no  small  measure  due  to  the 
stimulating  influence  of  the  rival  commodity. 


CHAPTER   I 
THE   PLANNING   AND   LAYING   OUT   OF   GASWORKS 

INTRODUCTORY 

The  public  supply  of  gas  in  this  country  is  governed  specifically  by  many  local 
Acts  of  Parliament,  and  in  general  by  the  Gasworks  Clauses  Acts  (1847  and  1871), 
the  Sale  of  Gas  Act  (1859)  and  the  Gas  and  Water  Works  Facilities  Acts  (1870  and 
1873).  In  addition,  London  companies  are  also  under  the  regulations  of  the  Metro- 
polis Gas  Act  of  1860.  A  statutory  company  has  powers  and  obligations  under 
its  own  special  Act  or  Provisional  Order,  as  well  as  being  governed  by  the  General 
Acts,  which  are  incorporated  therewith  as  a  whole  or  in  part.  A  Provisional  Order 
may  be  granted  to  a  non- statutory  company  under  the  Gas  and  Water  Works 
Facilities  Acts  authorizing  the  Company  to  supply  gas  and  conferring  the 
necessary  incidental  powers.  The  relation  of  such  a  non-statutory  company 
with  local  authorities  and  with  other  statutory  companies  is  similar  to  thc,t  of 
a  statutory  company. 

Statutory  companies  and  non-statutory  companies  having  powers  under  Pro- 
visional Orders  are  compelled  to  supply  gas  of  a  prescribed  quality  within  their 
denned  limits  of  supply,  and  are  usually  subject  to  the  infliction  of  certain  penalties 
if  the  conditions  as  to  the  purity  and  heating  or  illuminating  power  are  not  complied 
with.  Owing  to  the  extended  uses  of  gas  for  purposes  in  which  the  heating  value 
is  of  primary  importance,  Parliament  in  recent  years  has,  in  some  cases,  substituted 
a  calorific  test  for  the  formerly  universal  illuminating  test.  For  a  short  period 
the  Gas  Light  &  Coke  Company  had  the  dual  test,  but  were  relieved  of  the  older 
test  as  a  result  of  application  to  Parliament  during  Session  1914. 

In  many  cases  the  price  of  gas  to  consumers  is  graduated  on  a  sliding  scale 
basis,  in  accordance  with  which  the  dividend  paid  may  be  increased  above  a  certain 
standard  as  the  price  charged  is  decreased  below  an  accompanying  standard.  These 
two  figures  are  known  as  the  "  Standard  Price  "  and  "  Standard  Dividend,"  and 
in  the  case  of  an  increase  in  price  above  the  standard,  the  dividend  must  decrease. 

Parliament  fixes  this  standard  by  a  consideration  of  all  circumstances  tending 
to  affect  the  price  at  which  the  gas  can  be  produced,  plus  a  margin  for  contin- 
gencies. The  accompanying  dividend  is  fixed  with  regard  to  the  history  and  position 
of  the  company,  the  considerations  as  to  capital,  and  the  position  of  the  money 
market  at  the  time  of  the  application. 

Many  older  undertakings  are  governed  by  a  maximum  price  and  a  maximum 

4 


PLANNING  AND  LAYING  OUT  OF  GASWORKS    5 

dividend.  The  former  method  is  more  satisfactory  to  consumers  and  shareholders 
alike,  and  is  generally  adopted,  with  minor  variations,  in  all  new  Acts. 

In  making  application  to  Parliament  or  the  Board  of  Trade,  there  are  many 
Standing  Orders  and  ^Regulations  to  be  complied  with.  As,  however,  a  Parlia- 
mentary Agent  must  be  employed  to  pilot  the  Bill  or  Order  through  its  various 
stages,  the  engineer  or  manager  would  be  advised  of  all  such  requirements  coming 
within  his  (the  agent's)  province. 

A  non-statutory  company  operates  as  a  result  of  established  practice  or  under 
the  goodwill  of  the  local  authority.  In  opening  roads,  they  may  have  to  obtain  the 
sanction  of  more  than  one  local  authority,  e.g.  for  district  and  main  or  county  roads. 

A  non-statutory  company  sometimes  supplies  gas  within  the  area  of  a  statutory 
•company  without  molestation.  A  non-statutory  company  may  set  up  works  by 
permission  in  the  existing  area  of  a  statutory  local  authority,  or  if  already  in 
possession  when  a  statutory  authority  proposed  to  extend  its  limits,  may  continue 
to  operate  by  agreement.  Generally,  Parliament  will  respect  the  rights  of  a  non- 
statutory  company  in  such  circumstances,  and  will  not  grant  the  statutory 
company  the  extension  of  limits  unless  some  such  agreement  is  effected,  or  unless 
the  non-statutory  undertaking  were  bought  out  by  agreement  or  arbitration. 

Under  the  Public  Health  Act  of  1875,  a  local  authority  outside  the  Metropolis 
may  become  gas  supplier.  It  may  purchase  an  existing  undertaking  by  agreement,  or 
it  may  set  up  its  own  works  to  supply  the  whole  or  part  of  its  district.  The  latter 
proceeding  may  or  may  not  leave  another  concern  supplying  a  portion  or  portions 
of  its  district.  The  local  authority,  in  addition  to  supplying  its  own  ratepayers, 
often  supplies  a  much  wider  district.  The  price  charged  in  outlying  districts 
will  in  many  cases  be  greater  than  that  prevailing  in  the  inner  district,  both  in  the 
cases  of  companies  and  local  authorities. 

Purchase  may  be  effected  by  obtaining  a  "  Purchase  Clause  "  in  the  Bill  when 
the  company  is  applying  to  Parliament,  or  by  the  promotion  of  a  special  Bill,  which 
may  or  may  not  embody  other  powers.  Parliament  does  not  recognize  it  as  a 
universal  principle  that  the  undertaking  should  be  transferred,  and  the  local 
authority  must  bring  proof  either  that  there  has  been  serious  mismanagement 
in  the  past,  or  that  it  is  to  the  interest  of  the  ratepayers  and  consumers  that  they 
should  be  the  gas  authority. 

The  price  paid  for  any  such  transference  may  be  settled  by  agreement,  failing 
which  a  price  must  be  fixed  by  arbitration. 

The  local  authority  has  similar  powers  to  a  company,  but  has  a  greater  security 
when  raising  its  capital,  i.e.  the  financial  backing  of  the  rates  ;  but,  unless  expressly 
authorized,  it  cannot  supply  outside  its  own  area. 

A  local  authority  may  include  the  whole  of  a  neighbouring  district  in  its  area 
of  supply,  or  both  areas  may  be  supplied  by  a  Joint  Board. 

In  settling  the  price  paid  for  transference,  the  following  points  are  considered, 
amongst  others  : — 

(1)  Amount  of  maintainable  profit,  as  this  is  usually  the  basis  on  which  the 
concern  is  bought. 


6  MODERN   GASWORKS   PRACTICE 

(2)  Number  of  years'  purchase. 

(3)  Profit  on  fittings,  usually  capitalized  by  taking  three  to  five  years'  purchase. 

(4)  Whether  the  undertaking  is  statutory  or  non-statutory. 

(5)  Allowance  for  surplus  or  deficient  works. 

There  is  no  definite  rule  as  to  the  number  of  years  which  are  averaged  when 
dealing  with  the  maintainable  profit,  three  or  five  being  common  figures.  In 
arriving  at  the  maintainable  profit  the  following  considerations  vary  the 
amount  actually  shown  as  the  balance  of  the  Revenue  Accounts. 

(a)  Insufficient  or  excessive  repairs  and  renewals. 

(6)  Working  results  above  or  below  the  normal. 

(c)  Abnormal  conditions  regarding  prices  of  coal  or  residuals. 

(d)  Contracts  entered  into,  or  rights  and  privileges  affected  by  transference. 

(e)  Recent  scale  of  growth  and  prospects. 
(/)  Fairness  of  price  charged  for  gas. 

Goodwill  as  such  is  not  saleable,  although  item  (e)  covers  claims  for  future 
increased  profits.  The  term  of  years'  purchase  is  dependent  on  the  interest  which 
an  investor  can  get  with  equal  security.  The  period  varies  considerably,  ranging 
from  ten  to  thirty  years.  The  seller  rightly  claims  to  be  put  in  an  equally  good  position 
after  the  sale  ;  in  other  words,  he  must  earn  the  same  income  with  the  same  security. 

Anything  up  to  ten  per  cent,  is  added  for  compulsory  purchase  (where  it  is 
compulsory) ;  that  is,  for  interruption  of  tenure,  expense  and  trouble  in  seeking  new 
investments,  etc.,  but  this  is  usually  a  mere  matter  of  form.  Claims  may  be  made 
in  deductions  from  the  total  arrived  at  for  immediate  necessary  expenditure  to 
maintain  the  profit,  or  to  keep  the  undertaking  in  a  good  position  generally.  The 
structural  valuation  of  the  undertaking  has  little  bearing  on  the  price  paid,  and 
is  estimated  in  order  to  indicate  the  capital  assets  of  the  concern. 

It  should  be  mentioned  that  in  addition  to  the  General  Acts  named  at  the 
beginning  of  this  chapter,  the  sale  of  gas  in  Scotland  is  governed  by  the  Gas  Acts 
(1864),  and  the  Burghs  Gas  Supply  Acts  (1876  and  1893). 

The  supply  of  gas  in  Scotland  is  very  largely  in  the  hands  of  the  local  authori- 
ties, and  in  England  the  counties  of  Yorkshire,  Lancashire  and  the  North  generally 
are  much  more  marked  in  this  respect  than  the  Home  and  Southern  Counties. 
Whether  in  the  hands  of  companies  or  of  municipal  authorities,  however,  the  in- 
dustry as  a  whole  is  remarkably  well  managed,  and  is  on  a  firmer  basis  now  than 
ever  before  in  its  history.  Gas  for  all  purposes  has  ceased  to  be  a  convenience, 
and  has  become  a  necessity. 

THE   CHOICE   OF  A   SITE 

The  first  preliminary  to  the  erection  of  a  gasworks  is  the  selection  of  a  suitable 
site.  Although  this  task  may  appear  to  be  one  of  extreme  simplicity,  this  is  by 
no  means  the  case,  and  hasty  consideration  of  the  matter  may  have  a  lasting 


PLANNING   AND   LAYING   O]JT   QF   GASWORKS         7 

influence  on  the  welfare  of  the  undertaking.  The  more  important  points  to  be 
kept  in  view  may  be  summarized  as  follows  : —  . 

(a)  Ready  access  to  sea,  river,  canal  or  railway.  Cartage  to  and  from  the 
works  should,  as  a  general  principle,  be  avoided  as  far  as  possible,  and  works  having 
a  combination  of  water,  rail  and  road  facilities  enjoy  an  enviable  position.  This 
accessibility  has  a  twofold  value,  viz.  :  in  getting  coal  and  other  materials  into 
the  works  and  in  the  taking  away  of  residuals.  Generally,  it  may  be  taken  that 
good  sea  or  river  access  is  preferable  to  rail. 

With  reference  to  the  last  mentioned,  the  actual  construction  of  sidings  is  a 
financial  matter,  depending  entirely  on  the  money  to  be  saved  balanced  against 
the  annual  charges  for  construction,  working  and  incidental  costs  payable  to  the 
railway  company. 

(6)  The  level  of  the  ground  should  be  low  in  comparison  with  the  districts 
to  be  supplied.  It  is  a  "  golden  rule  "  of  gas  engineering  never  to  erect  a  gasworks 
on  a  hill.  Owing  to  its  specific  gravity  (042  to  0-52,  depending  on  the  proportion 
of  carburetted  water  gas),  gas  exerts  its  pressure  in  an  upward  direction ;  hence 
where  the  works  is  erected  on  elevated  ground  unnecessary  pressure  has  to  be  sacri- 
ficed in  driving  the  gas  downwards  to  consumers.  With  regard  to  the  so-called  loss 
in  pressure,  this  amounts  approximately  to  1  inch  of  water  for  every  ICO  feet  rise 
in  elevation.  There  are  generally,  of  necessity,  many  .points  lower  than  the,  gas- 
works, especially  in  undulating  country,  but  in  general,  keep  low,  having  regard 
to  other  matters  mentioned  later  with  reference  to  flooding. 

(c)  The  character  of  the  surrounding  property  must  be   considered.      A  gas- 
works is   essentially  a  thing  of   utility,  and  can  lay  little  claim  'to   aestheticism ; 
therefore  the  picturesque  portions  of   the    district  should  be  respected.     For  the 
same  reason,  a  site  should  not  be  chosen  in  the  fashionable  quarter  of  the  town, 
otherwise    complaints    from   well-to-do   residents  will  be   a    continual    source  of 
annoyance. 

Here  it  may  be  mentioned  that  when  applying  for  parliamentary  sanction 
to  make  or  purify  gas  on  any  land,  notices  have  to  be  served  on  all  owners,  lessees 
and  occupiers  of  dwelling  houses  within  SCO  yards  of  any  portion  of  the  said  land, 
who  may  petition  the  House  (before  Committee)  against  the  adoption  of  the  site. 

(d)  The  ground  should  be  suitable  for  foundations,  both  as  to  cost  and  stability. 
Before  a  definite  agreement  is  concluded,  trial  borings  should  be  made,  and  the 
nature  of  the  subsoil  determined.     Hard  gravel,  ballast  and  chalk  are  the  ideal. 
Many  clays  form  excellent  foundations,  whilst  "  made  up  "  ground  (such  as  disused 
rubbish  heaps,  tips,  etc.)  is  probably  the  most  treacherous.     Running  sand,  com- 
pressible clays,  soft  peat  and  fine  alluvial  soil  may  turn  out  to  be  very  untrustworthy 
and  costly.    'Rock,  of  course,  makes  excellent  foundations,  but  is  expensive  to 
work,  although  it  may  be  used  for  concrete  mixing.     Further  economy  may  be 
effected  by  obtaining  sand  or  ballast  from  the  ground, 

Of  extreme  importance  is  the  permanent  water  level,  and  the  possible  floods 
level ;  both  affect  the  cost  of  works  construction,  the  former  in  particular.  The 
latter  affects  the  actual  operation  of  the  works,  for  no  gasworks  can  be  called 


8  MODERN   GASWORKS   PRACTICE 

factory  if  always  liable  to  floods.  The  loss  of  tar  and  liquor  from  underground 
wells  would  be  considerable  and  the  damage  to  buildings  and  plant  would  be  heavy, 
but  the  greatest  danger  would  be  that  of  complete  stoppage  by  the  extinguishing 
of  furnaces  in  the  retort  house.  These  points  are  more  fully  dealt  with  in  Chapter 
II  (Foundations). 

A  plentiful  supply  of  water  under  control  is,  of  course,  an  economic  asset,  effect- 
ing a  considerable  annual  saving. 

(e)  The  distance  of  the  site  from  the  centre  of  the  area  of  greatest  consumption 
is  a  further  point.  The  works  need  not  necessarily  be  erected  within  its  own  limits 
of  supply,  although  it  almost  invariably  is.  Owing  to  high  cost  of  land  near  the 
centre  of  towns,  the  gasworks  is  usually  situated  on  the  outskirts,  or  what  were 
the  outskirts  when  the  works  was  erected.  In  such  cases,  of  course,  the  additional 
length  of  trunk  mains  must  be  balanced  against  the  saving  in  cost  of  land,  and  the 
sale  of  residuals  and  cartage  costs  must  in  general  be  considered.  For  long  distance 
transmission,  modern  methods  by  means  of  "  boosters  "  may  be  employed,  per- 
mitting the  use  of  smaller  and  therefore  cheaper  trunk  mains.  Needless  to  say,  the 
high  pressure  must  be  governed  down  for  ordinary  purposes.  It  often  happens 
(after  considerable  growth)  that  storage  plant  has  to  be  erected  further  out  of  the 
town,  so  that  the  central  site  may  be  occupied  for  manufacture  and  purification. 
A  minor  factor  requiring  consideration  is  the  possible  danger  of  pollution  to  the 
water  supply  by  percolation,  particularly  in  chalky  districts. 

CONSIDERATIONS   AFFECTING   SIZE   OF   WORKS 

Before  much  headway  can  be  made  with  the  actual  definition  of  the  site  boun- 
daries, some  idea  as  to  the  extent  of  the  ground  required  must  be  arrived  at,  this, 
of  course,  being  dependent  upon  the  quantity  of  gas  likely  to  be  consumed  imme- 
diately and  during  the  next  fifteen  or  twenty  years.  It  is  as  well  to  be  generous 
in  the  purchase  of  land,  particularly  if  it  is  cheap  ;  and  preference  should  be  given 
to  a  site  which  is  capable  of  extension.  A  square  or  rectangular  site  is  the  most 
suitable  for  laying  out  buildings  and  plant. 

As  regards  the  quantity  of  land  to  be  purchased,  experience  is  really  the  only 
reliable  guide ;  so  much  depends  upon  the  nature  of  the  district  to  be  supplied, 
whether  residential  or  manufacturing,  the  class  of  inhabitant,  presence  or  absence 
of  electrical  competition,  and  the  price  at  which  gas  is  intended  to  be  sold.  In 
this  respect  sales  of  gas,  unlike  water,  cannot  be  satisfactorily  calculated  by  an 
allowance  of  so  much  per  head  of  population ;  for,  although  every  individual  may 
be  credited  with  a  desire  for  water,  the  same  cannot  always  be  said  of  gas.  As  a 
matter  of  fact,  in  the  larger  cities  the  average  consumption  per  head  per  annum 
is  from  5,500  to  10,000  cubic  feet,  whilst  in  the  smaller  towns  it  may  be  from  3,000 
to  7,500  cubic  feet.  Fifteen  years  ago  it  was  a  general  rule  to  base  the  former  at 
2,000  cubic  feet  per  head  and  the  latter  at  1,600  cubic  feet. 

The  table  will  give  some  idea  as  to  how  matters  stood  prior  to  the  European 
war : — 


PLANNING  AND  LAYING  OUT  OF  GASWORKS 


Cubic  feet 
per  head. 

Cubic  feet 
per  consumer. 

Sale  in 
millions  per 
annum. 

Price. 

Birmingham  
Alanchester 

10,200 

7,200 

47,500 
27,200 

9,156 
5,659 

s.     d. 
1   11  less 
2     2 

5%* 
2d  * 

Nottingham  
Leeds  

7,600 
6,100 

26,000 
20,900 

2,169 
2,723 

2    2 
2     2  less 

5°/n* 

York  

5,800 

23,200 

540 

2     1 

Brighton  
Hastings  
Guildford  
Watford  
Canterbury  

7,700 
5,600 
7,200 
5,700 
5,700 

31,000. 
34,800 
30,200 
26,800 
25,200 

1,450 
475 
195 
291 
150 

2  10 
2  10J 
2     8 

20 
o 

2     8 

Longwood  

4,600 

19,000 

130 

2     5 

*  Discount  applied  to  accounts  paid  within  one  month. 

From  an  estimating  standpoint,  the  second  column  of  figures  is  the  most  useful, 
for,  taking  all  considerations  into  account,  the  number  of  consumers  and  their 
average  can  be  fairly  closely  approached  by  anyone  of  experience.  The  figure  in 
the  column  referred  to  includes  public  lighting,  treating  each  lamp  as  a  consumer. 
In  the  general  way,  a  very  good  idea  of  the  total  probable  output  can  be  gleaned 
from  an  analysis  of  the  situation  on  lines  such  as  the  following  : — 

Suppose  that  the  town  to  be  supplied  consists  of  a  middle  class  and  normal 
residential  population  (seaside  resorts  have  to  take  into  account  the  summer  influx 
of  visitors)  with  trades  and  industries  of  its  own.  For  the  sake  of  example,  assume 
a  normal  population  of  90,000,  then  with  gas  at  a  moderately  low  price,  about  17 \ 
per  cent,  of  the  population  may  be  expected  as  consumers,  made  up  as  follows  : — 

Say  17,500  to  18,500  houses,  of  which  the  mains  to  be  laid  would  permit  of 
access  to  17,000  or  so.  In  the  circumstances,  90  per  cent,  of  these  may  be  expected, 
or  15,500. 

Then  the  estimated  amount  of  gas  to  be  sold  per  annum  would  be  : — 


6,500  consumers  through  ordinary  meters  at  42,000 
8,500  „  „        "slot"  „          15,000 

For  industrial  purposes  extra  (say  500  consumers) 
For  public  lighting  (1,200-1,500  lamps). 


Cubic  Feet. 
Millions. 

.  273 

.  127 

.  60 

.  20 

480 


In  addition  to  this  sale,  about  6  per  cent,  must  be  allowed  for  gas  lost  by 
leakage  and  gas  used  on  the  works.  This  brings  the  annual  production  up  to  508 
millions,  or,  in  round  figures,  500  millions.  The  sale  per  head  then  works  out  at 
nearly  5,500  cubic  feet,  or  30,OCO  cubic  feet  per  consumer,  excluding  public  lighting  ; 
which,  on  reference  to  the  table,  is  seen  to  be  normal,  and  satisfactory  for  estima- 
ting purposes. 


10  MODERN   GASWORKS   PRACTICE 

AMOUNT   OF   LAND   REQUIRED 

In  considering  ground  area  required,  much  depends  on  the  manufacturing 
system  it  is  proposed  to  employ,  but  a  good  guide  is  to  allow  a  minimum  of  2 
acres  per  million  cubic  feet  per  diem.  So  far  as  the  maximum  day's  send  out  is 
concerned,  this  is  now  found  to  amount  to  1/220  or  1/230  of  the  whole  year's  con- 
sumption. That  is  in  normal  cases,  apart  from  health  resorts  or  towns  having  a 
double  heavy  season. 

Ten  years  ago  this  ratio  varied  from  1/185  to  1/210  ;  so  that  it  is  now  possible 
to  sell  from  10  to  15  per  cent,  more  gas  with  identical  plant,  owing  to  the  levelling 
up  of  the  daily  load  curve.  In  the  same  manner  the  hourly  load  curve  has  also 
been  appreciably  straightened  out,  thus  saving  many  undertakings  considerable 
expense  in  gasholder  construction. 

In  the  example  taken  we  get  a  maximum  day's  production  of  500/220  millions 
per  day  =2-3  millions.  So  that  land  and  plant  must  be  at  least  equal  to  this  pro- 
duction. 

Land  required  =2-3x2  =4-6,  say  5  acres.  More  than  this  is  needed  if  the 
works  is  to  be  planned  with  a  view  to  easy  and  economical  extension,  a  point  of 
great  importance  in  the  works  design.  Also,  more  land  generally  means  greater 
economy  in  working.  It  is  interesting  to  note  that  twenty  years  ago  the  late  Mr. 
A.  Colson  expressed  the  view  that  2|  acres  were  required  per  million  per  day  as  a 
minimum.  Since  then,  however,  the  gas-producing  capacity  of  a  given  area  has 
considerably  increased,  although  the  remainder  of  the  plant  (except  gasholders) 
has  undergone  very  little  change  so  far  as  necessary  ground  space  is  concerned. 

CAPITAL  EXPENDITURE 

The  capital  expenditure  likely  to  be  entailed  in  the  erection  of  a  gasworks 
and  the  equipment  of  the  district  is  difficult  to  compute  with  any  degree  of  accuracy 
until  the  site  is  selected  and  preliminary  survey  and  estimates  have  been  made. 
So  much  depends  on  the  prevailing  value  of  materials  of  construction,  the  require- 
ments of  labour,  the  geographical  position  of -the  town,  facilities  for  conveying  mate- 
rials to  the  site,  etc.,  that  no  hard  and  fast  rule,  applicable  to  all  cases,  can  be  given. 

In  preliminary  estimates,  for  parliamentary  and  other  purposes,  it  is  advisable 
to  allow  a  fair  margin  to  cover  possible  increases  in  cost,  as  the  work  may  be  carried 
out  as  long  as  two  years  after  the  preparation  of  the  estimate. 

In  general,  however,  a  concern  promoted  for  the  erection  of  a  modern  works, 
and  for  providing  the  distribution  plant  necessary  to  sell  the  gas,  should  find  it  pos- 
sible to  complete  the  scheme  for  £600  per  million  cubic  feet  sold  per  annum,  i.e.  12s. 
per  thousand  cubic  feet  sold  per  annum.  In  the  case  of  the  larger  works,  the  figure 
may  be  reduced  to  £550  or  less,  but  for  the  smaller  country  works  the  outlay  will 
usually  be  considerably  greater,  a  normal  figure  being  as  much  as  £750  to  £1,000 
per  million  cubic  feet  sold,  according  to  size. 

Capital  expenditure  based  on  output  in  this  manner  should,  with  proper  man- 
agement, decrease  as  years  go  on,  chiefly  due  to  the  taking  up  of  increased  business 


PLANNING  AND   LAYING   OUT   OF   GASWORKS      11 


with  existing  plant,  or  by  only  slight  additional  expense  for  considerably  augmented 
consumption.  A  judicious  expenditure  out  of  revenue  to  increase  the  efficiency 
of  the  plant  and  mains  is  an  aid  to  this  desirable  end  ;  for  it  must  be  borne  in  mind 
that  capital  expenditure  is  usually  the  very  crux  of'  a  company's  condition.  In 
nine  cases  out  of  ten,  the  capital  charge  to  be  met  is  the  heaviest  item  (proportionally) 
in  the  revenue  account. 

As  an  example  of  this  tendency,  and  the  improvement  effected  by  expansion 
of  business,  the  average  capital  expenditure  by  the  three  metropolitan   companies 


In  June,  1906 

In       „  1910 

In      „  1912 

In  Dec.,  1913 


11s.  2d.  per  thousand  cubic  feet  sold. 
10s.  9d.     „ 
10s.  2d.     „ 
10s.  Id. 


The  following  figures  give  an  indication  of  this  item,  and  its  relation  to  various 
companies  and  corporations  : — 

(All  figures  relate  to  the  period  just  prior  to  the  European  war.) 


1 

£  Per  million 
cubic  feet  sold 
per  annum. 

Shillings  per  thou- 
sand cubic  feet  sold 
per  annum. 

COMPANIES. 
Gas  Light  and  Coke  

£ 
546 

s.    d. 
10  11 

South  Metropolitan     
Brighton      

387 
462 

7    9> 
9     3 

Derby    .            

479 

9     7 

Bath       

362 

7     5 

Hastings-     .      

862 

IT    3 

Newcastle    

759 

15    2 

Sutton   

454 

9     1 

Watford      .      

487 

9    9 

Reading 

483 

9    & 

Longwood  . 

660 

13    3 

CORPORATIONS. 
Birmingham     

283 

5     & 

Manchester       

525 

10     6. 

Leeds     ....      

692 

T3  10" 

Nottingham      ... 

546 

10  11 

Leicester      

638 

12     9 

In  recent  years  the  capital  expenditure  on  the  district  has  increased  rapidly, 
owing  to  the  development  of  the  prepayment  meter  business  and  the  greatly  extended 
use  of  gas  cookers,  fires,  geysers,  etc.  The  first-named  item  of  expense  is  con- 
sidered as  varying  from  £3  10s.  to  £5  10s.  per  house  (including  cooker),,  but  excluding 
service,  which  is  common  to  all  classes  of  consumer.  The  consumption  for  this 
expense  may  be  from  7,000  to  22,000  cubic  feet  per  annum ;  and,  averaging  these-. 


12  MODERN   GASWORKS   PRACTICE 

figures,  we  get  an  expenditure  of  £310  per  million  on  the  gas  sold  through  this 
channel.  There  is,  of  course,  an  increased  receipt  from  this  source,  which  may  or 
may  not  give  an  adequate  return  on  the  capital,  after  allowing  for  extra  cost  of  col- 
lection, repairs,  and  maintenance. 

The  result  is  that,  whereas  twenty  years  ago  the  works  usually  cost  more  than 
the  distributing  plant,  the  reverse  is  now  invariably  the  case.  Keeping  in  mind, 
however,  the  general  example  we  are  considering,  the  cost  of  mains,  meters,  stoves, 
etc.,  comprising  the  distributing  plant,  may  absorb  55  per  cent,  of  the  total,  the 
works  and  equipment  amounting  to  38  per  cent.,  whilst  engineers'  fees,  parlia- 
mentary and  promotion  expenses  complete  the  total.  A  fact  not  generally  realized 
with  regard  to  works  outlay  is  that  the  expense  of  gasholders  in  many  cases 
accounts  for  one-fourth  or  even  one- third  of  the  total,  and  is  the  most  expensive  in- 
dividual item  on  the  works.  The  remainder  is  apportioned  somewhat  as  follows  : — 

Land          .         .         .         .         .         .  •*  .  2-4     per  cent,  of  works  expenditure. 

Carbonizing  plant  (including  buildings)  .  20-27£  „       „  „  „ 

Purifying  plant  .         .          .          .  .  5-8       „       „  „  ,, 

Exhausters,  condensers,  washers,  etc.  ..       3-4       „       „  „  „ 


Gasworks  are  never  designed  by  rule-of-thumb  methods,  and  the  details  con- 
nected with  their  construction  are  mostly  the  outcome  of  extended  practical  experi- 
ence. For  all  that,  certain  constants  for  the  computation  of  the  capacity  of  the 
various  pieces  of  plant  have  come  to  be  recognized,  and  are  given  here  with  the 
strict  warning  that  they  are  merely  a  guide,  exemplifying  rules  and  their  application. 
Varying  circumstances  alter  cases,  and  in  laying  out  the  works  all  those  circum- 
stances should  be  taken  into  account  which  would  tend  to  vary  sizes  from  the  normal. 
Although,  in  the  main,  the  rules  given  will  be  found  as  occurring  in  general  practice, 
the  author  wishes  to  deter  the  aspiring  designer,  with  little  or  no  actual  experience 
of  gasworks  erection,  from  drawing  up  specifications  on  such  a  basis  alone. 

LAND 

Allow  at  least  2  acres  per  million  cubic  feet  per  maximum  day. 

RETORT  HOUSE 

Dependent  upon  the  gas-making  capacity  of  each  "  unit,"  i.e.  the  batch, 
of  retorts  set  in  each  arch.  The  following  table  gives  approximate  figures  for  the 
make  per  retort  per  day  of  twenty-four  hours  : — 

•Stop-ended  retorts,    9  feet  to  10  feet  long  X  15  inches  round  .     3,000-4,000  cubic  feet. 

„      10  feet  long  X  16  inches  round  .          .  .     4,000-5,500  „ 

„  „      10  feet  long  X  21  inches  X  15  inches  Q   }  000-8  500 

or  10  feet  long  X  22  inches  X  16  inches  Q    j 

•"  Through  "  retorts,  20  feet  long  X  24  inches  X  16  inches  Q  .    18,000-20,000  „ 

Tertical  retorts,  Woodall-Duckham  type  .  60,000  „         „ 

Glover-West  type 36,000  „ 

„  „        Intermittent  (Dessau)  type  (5  metres  long)     .  15,600  „         „ 


PLANNING   AND   LAYING   OUT   OF   GASWORKS       13 

Instead  of  speaking  of  the  make  per  retort  per  diem,  it  is  usual  among  gas 
engineers  to  work  on  a  basis  of  "  make  per  mouthpiece  "  per  diem.  This  is  particu- 
larly the  case  with  horizontal  and  inclined  retorts ;  thus  the  "  make  per  mouth- 
piece "  for  a  stop-ended  retort  would  be  3,000  to  8,500  cubic  feet,  the  same  as  the 
make  per  retort.  For  a  "  through  "  retort  it  varies  from  about  7,500  to  10,COO 
cubic  feet,  i.e.  half  the  make  per  retort,  this  being  due  to  the  fact  that  the  retort 
has  two  mouthpieces — one  at  each  end. 

COAL  STORAGE 

It  is  customary,  and  it  has  been  found  advantageous,  to  provide  for  storage 
under  cover  sufficient  for  twenty-one  maximum  days'  production.  In  recent  years, 
owing  to  the  unsettled  condition  of  the  labour  market,  the  larger  companies  have 
in  many  cases  sufficient  supplies  for  their  needs  for  three  months ;  hence  recourse 
has  to  be  had  to  stacking  large  heaps  out  in  the  open.  No  undertaking  can  now 
afford  to  risk  three  weeks'  storage,  although  this  is  still  a  common  and  sufficient 
allowance  for  that  kept  under  cover.  The  calculation  of  the  cubical  capacity  required 
for  storing  a  definite  quantity  of  coal  may  be  closely  arrived  at  by  assuming  that 
1  ton  of  average  gas  coal  occupies  42  to  43  cubic  feet  of  space.  One  ton  of  gas 
coke  requires  a  space  of  about  85  cubic  feet.  Coal  should  not  be  stacked  to  a  greater 
depth  than  20  feet,  owing  to  the  danger  of  spontaneous  combustion. 

CONDENSERS 

Owing  to  the  many  advantages  attendant  upon  the  use  of  water  condensers, 
they  are  now  frequently  employed  in  preference  to  the  original  atmospheric  type  ; 
the  latter,  however,  are  still  used  in  small  and  medium-sized  works,  and  are  not 
without  their  good  points.  It  should  be  remembered  that  the  initial  stages  of 
condensation  should  be  effected  slowly. 

There  are  several  rules  for  the  capacity  of  air  condensers,  and  the  variable 
nature  of  the  results  they  give  shows  that  engineers  are  by  no  means  agreed  on  the 
subject.  A  common  and  reliable  rule  is  the  following : — 

Allow  5  square  feet  of  atmospheric  condensing  surface  per  1,CCO  cubic  feet  of 
gas  made  per  day  (maximum  day's  production  to  be  taken).  This  area  includes  all 
pipe  from  the  outlet  of  the  hydraulic  main  to  the  outlet  of  the  condenser,  and  permits 
of  a  small  deduction  being  made  if  there  is  a  further  long  distance  to  the  inlet  of  the 
exhauster.  Various  authorities  recommend  increasing  surfaces  up  to  nearly  double 
this  amount. 

Regarding  water-cooled  condensers,  there  is  considerable  variation,  according 
to  type,  amount  and  speed  of  water  circulation,  etc.,  but  for  general  purposes  about 
3  square  feet  per  1,000  cubic  feet  per  day  should  be  allowed,  i.e.  about  one-half 
of  that  necessary  with  the  atmospheric  type. 

EXHAUSTERS 

Except  on  very  small  works,  say  less  than  10  or  12  millions,  the  exhausting 
plant  is  generally  laid  down  in  duplicate,  to  allow  of  repairs  or  adjustments  to  one 


14  MODERN   GASWORKS   PRACTICE 

set.  A  useful  combination  for  medium-sized  works  is  one  set  equal  to  the  maximum 
winter's  production  and  the  second  equal  to  that  of  the  summer.  It  should  be 
remembered  that  the  cost  price  of  exhausting  machinery  increases  at  an  appre- 
ciably slower  rate  than  capacity ;  hence  it  is  often  convenient,  and  in  a  growing 
place  absolutely  necessary,  to  lay  down  exhausters  in  excess  of  immediate  require- 
ments. Slower  running  of  an  under- taxed  exhauster  will  always  make  for  smoother 
work  and  longer  life. 

In  a  works  of  4  to  6  millions  per  annum  the  saving  to  be  effected  in  purchasing 
an  exhauster  is  problematical,  after  paying  interest  on  capital  and  running  costs. 
For  works  over  6  millions  the  buyer  is  on  safe  ground,  and  in  such  works  (say  less 
than  15—20  millions)  it  is  usual  to  drive  by  gas  engine,  which  provides  power  for 
operating  tar,  liquor  and  other  pumps.  If  working  to  exact  capacities,  it  is  merely 
necessary  to  take  a  very  small  margin  over  the  maximum  day's  production,  which  is 
arrived  at  by  dividing  the  yearly  production  by  220.  The  maximum  day  divided 
by  20  or  22  will  give  the  maximum  hour,  which  is  the  usual  way  of  tabulating 
exhauster  capacities.  The  effective  hourly  capacity  of  an  exhauster  is  guaranteed 
by  the  makers,  and  reference  to  catalogues  gives  all  particulars  relating  to  standard 
sizes,  space  occupied,  etc. 

For  the  capacity  of  a  four-blade  exhauster,  the  following  formula  may  be  taken  ; 
it  is  not,  however,  recommended  when  dealing  with  very  large  (over  4  feet)  or  very 
small  exhausters  : — 

Q  -  65  D2  L.N. 

Where  Q  —  cubic  feet  passed  by  exhauster  per  hour. 
D  =  inside  diameter  of  outer  drum  in  feet. 
L  =  length  of  drum  in  feet. 
N  =  number  of  revolutions  per  minute.. 

About  20  per  cent,  of  the  amount  arrived  at  must  then  be  deducted  for  "  slip." 
The  power  necessary  to  drive  exhausters  is  dependent  on  their  capacity  and  the 

total  back  pressure  to  be  overcome.     (See  Chapter  XIII.)    This  necessary  power  at 

the  shaft  needs  a  little  more  at  the  engine,  the  extra  being  dependent  on  the  method 

of  driving,  whether  direct  coupled  or  through  shafting. 

Generally,  however,  the  maker  has  a  standard  engine  to  a  certain  sized  exhauster, 

leaving  sufficient  margin,  and  unless  stated  otherwise  by  the  purchaser,  this  standard 

size  will  be  supplied. 

WET  PURIFICATION  PLANT 
This  may  include  one,  two,  or  three  of  the  following  types  of  plant : — 

Tower  scrubber. 
Livesey  type  washer. 
Mechanical  washer. 
Washer-scrubber. 
Purifying  machine. 

The  last  mentioned  includes  one  or  two  makes  of  mechanical  apparatus  which 


PLANNING   AND   LAYING   OUT   OF   GASWORKS       15 

remove  both  tar  and  ammonia.  The  washer-scrubber  is  mechanical,  and  the  many 
different  patterns  conform  to  one  general  type.  Livesey  washers,  made  by  many 
firms,  are  not  mechanical ;  and  the  first  mentioned  in  the  list  is  usually  fed  with 
water  or  liquor  by  mechanical  means.  In  many  cases  two  pieces  of  plant  in  the 
above  list  are  associated  with  a  tar  extractor  of  the  Pelouze  pattern.  By  far  the 
most  common  combination  is  a  mechanical  washer-scrubber  followed  by  one  or  more 
tower  scrubbers.  If  two  are  adopted,  the  last  is  fed  with  clean  water,  which 
should,  if  desired,  remove  the  whole  of  the  ammonia. 

In  small  works,  it  is  common  to  have  only  one  or  two  tower  scrubbers,  with  no 
mechanical  washing  apparatus  whatever.  When  associated  with  a  mechanical 
apparatus,  the  scrubber  allowance  should  be  at  least  equal  to  5  or  6  cubic  feet  per 
1,000  cubic  feet  of  gas  per  day.  Newbigging  and  Herring  recommend  9  cubic  feet. 
In  cases  where  no  washer -scrubber  is  employed,  the  aggregate  capacity  of  ordinary 
washers  and  scrubbers  must  be  increased  to  10  cubic  feet  per  1  ,CCO.  In  very  small 
works  where  only  one  tower  scrubber  is  used,  this  figure  might  with  advantage  be 
increased  to  12  cubic  feet.  The  ratio  of  the  height  of  a  scrubber  to  its  diameter 
varies  in  normal  cases  from  1\  to  5. 

With  regard  to  the  other  forms  of  apparatus  mentioned,  each  manufacturer 
has  his  own  standard  sizes  of  plates  for  varying  capacities,  but  as  a  general  guide 
the  following  figures  will  be  found  useful : — 

Livesey  washers        .         .          .          .     \-\  cubic  feet  per  1,000  cubic  feet  per  day. 
Washer-scrubbers     ....     £-£      „         „       „       „          „         „       „         „ 

DRY  PURIFICATION  PLANT 

If  it  is  necessary  or  desirable  to  remove  sulphur  compounds  other  than  sul- 
phuretted hydrogen,  the  purifier  capacity  is  increased,  this  usually  calling  for 
the  use  of  lime  in  addition  to  oxide  of  iron  (or  its  equivalent).  Under  such  circum- 
stances it  is  advisable  to  increase  slightly  the  size  of  the  vessels,  as  well  as  further 
increasing  the  capacity  by  means  of  catch  boxes.  It  should  be  remembered  that 
if  more  area  can  be  given  than  in  the  following  rules,  it  is  never  wasteful,  purification 
charges  undergoing  reduction,  whilst  the  first  cost  of  the  plant  increases  slowly 
as  compared  with  the  capacity.  In  other  words,  the  smaller  the  boxes  the  more 
expensive  do  they  become  per  unit  of  purifying  capacity.  For  oxide  purification 
only  (for  a  set  of  four  purifiers)  an  area  of  0-5  square  faat  per  1,000  cubic  feet  per 
day  should  be  provided  as  a  minimum  in  each  box.  If  lime  is  used  this  figure  should 
be  increased  to  0-6  square  foot,  or  to  0-65-0-7  if  no  catch  boxes  are  provided.  For 
the  total  amount  of  purification  space  necessary  (i.e.  the  combined  area  of  all  boxes) 
the  rule  given  by  Hunt  is  useful.  This  states  that  for  lime  and  oxide  purification 
20  to  30  square  feet  per  ton  of  coal  carbonized  per  day  should  be  allowed. 

A  further  rule,  based  on  the  amount  of  oxide  in  the  boxes,  is  that  one  ton  of 
oxide  may  be  expected  to  purify  about  2  million  cubic  feet  of  gas  before  becoming 
finally  spent. 

The  maximum  figure  can  only  be  obtained  when  air  is  put  into  the  boxes  for 


16 

revivification.  A  further  rule  is  that  for  each  1,OCO  cubic  feet  of  gas  per  day  allow 
1J  to  2  cwts.  of  oxide  in  each  of  four  boxes. 

In  designing  plant  for  a  growing  works,  it  is  necessary  to  provide  for  the  more 
or  less  immediate  future,  and  it  is  advisable  to  erect  only  three  boxes,  making  provision 
for  the  easy  addition  of  the  fourth.  In  this  case  the  boxes  in  the  set  of  three  should 
be  made  50  or  60  per  cent,  larger  than  those  necessary  in  a  set  of  four  (say  0-8-0-85 
square  foot  per  1,000  cubic  feet  per  day  for  the  area  of  each  box).  In  the  case  of  a 
very  small  works  with  prospect  of  growth,  two  boxes  with  facilities  for  extension 
can  be  put  in  with  advantage,  in  which  case  each  box  should  be  made  3-3£  times  as 
large  as  if  there  were  four  (1-5  to  1-7  square  feet  per  box  per  1,000  cubic  feet  per 
day).  By  adopting  this  plan  the  first  cost  is  not  increased,  and  money  is  saved  when 
extensions  are  carried  out. 

The  size  of  conne3tions  for  purifiers  may  be  calculated  as  follows  : — 

Diameter  of  pipes!          /-r-      — =—  — ^- 

•     •     ,  t  =  A/ Area  of  each  box  in  square  feet. 

For  small  purifiers  make  no  deduction  from  the  figure  so  found,  but  in  large  and 
medium  sized  boxes  deduct  -g-  to  J. 

Small  boxes  are  from  3  to  4  feet  deep,  and  large  ones  may  run  from  6  to  8  feet, 
6  feet  being  most  common.  The  intermediate  sizes  vary  from  4  to  6  feet  in  depth. 
Purifiers  vary  in  size  from  12  square  feet  in  area  up  to  40  feet  square,  the  latter  size 
being  suitable  for  a  2f  to  3  million  cubic  feet  a  day  unit.  For  constructional  reasons, 
convenience , in  working,  lifting  covers,  emptying,  etc.,  when  the  works  is  larger  than 
this  it  becomes  necessary  to  divide  the  gas  into  streams,  each  with  its  own  set  of 
boxes.  In  works  making  less  than  2|  to  3  millions  per  day  this  system  is  also  in 
operation  owing  to  development  in  the  past,  and  it  is  very  useful  where  different 
sized  units  are  in  use,  the  larger  set  being  operated  in  summer  and  both  sets  in 
winter. 

Thus  a  3  million  a  day  works  would  have  35  or  36  feet  boxes  for  its  larger  unit 
and  24  feet  boxes  for  the  smaller  unit.  The  former  unit  would  probably  be  suffi- 
cient for  eight  months  in  the  year,  and  both  sets  would  be  in  use  for  the  remaining 
four  months.  The  larger  set  would  then  take  27-inch  connections  and  the  smaller 
18-inch  to  20-inch. 

For  carburetted  water-gas  purifiers  it  is  advisable  to  take  0-8  square  foot  per 
1,000  cubic  feet  per  day  for  each  box,  again  assuming  four  boxes  to  the  set. 

GOVERNOES 

Dependent  entirely  on  the  nature  and  conditions  of  the  district  to  be  supplied. 
Absolutely  no  rules  can  be  given  attempting  to  cover  more  than  the  simplest  possible 
case,  i.e.  a  level  district,  with  the  gas  sold  in  one  centre,  in  which  instance  the  one 
necessary  governor  is  of  the  same  size  as  the  main  outlet  pipe  from  the  works. 

STORAGE  CAPACITY 

The  levelling  up  of  the  hourly  load  curve  in  recent  years  has  had  a  marked  effect 
on  the  amount  of  storage  necessary.  In  spite  of  considerable  increases  in  annual 


PLANNING  AND   LAYING   OUT   OF   GASWORKS       17 

sales,  none  of  the  three  metropolitan  companies  has  built  a  gasholder  for  many 
years,  and  as  the  South  Metropolitan  Company  is  here  included,  the  question  of 
storage  cannot  be  due  entirely  to  the  use  of  carburetted  water  gas,  although  it  is 
naturally  influenced  by  the  presence  and  capacity  of  the  water-gas  plant.  The  other 
factor  affecting  the  storage  required  is  the  nature  of  the  supply,  whether  chiefly 
lighting,  or  power,  or  cooking  ;  the  last  two,  if  in  large  quantities,  causing  the  peak 
to  be  from  11.30  a.m.  to  1.30  p.m.,  or  thereabouts,  instead  of  during  the  evening. 

Where  the  load  curve  is  assisted  in  this  manner  and  surplus  water  gas  is  available, 
the  storage  can  safely  be  reduced  to  18  hours'  maximum  make.  Otherwise  21-24 
hours'  should  be  provided  for.  It  is  as  well  not  to  rely  on  the  surplus  water-gas- 
plant  other  than  as  a  means  for  meeting  emergencies,  such  as  fogs  or  breakdown  in 
coal-gas  plant.  With  reference  to  ground  space  occupied,  it  may  be  mentioned  that 
gasholders  require,  roughly,  20  per  cent,  more  room  than  the  combined  retort- 
houses  and  coal  stores,  under  normal  conditions. 

It  will  be  understood  that  the  storage  capacity  on  the  daily  make  basis  is  very 
elastic,  as  the  newest  holder  is  almost  invariably  the  largest ;  consequently  before  this 
is  put  into  operation  the  storage  is  deficient,  whilst  immediately  afterwards  it  may 
be  excessive,  provision  being  made  for  the  future. 

A  common  method  of  providing  for  future  development  is  to  build  the  tank 
and  one  or  more  lifts  with  all  arrangements  for  adding  a  further  (outer)  lift  in  the 
future.  Thus  the  capacity  of  such  a  holder  may  be  increased  from  50  to  ICO  per 
cent,  with  a  comparatively  small  expenditure.  It  must  be  remembered,  however, 
that  this  method  cannot  be  adopted  where  one  holder  is  relied  upon,  or  where  the 
other  storage  is  so  small  that  it  cannot  be  reduced  even  in  the  slackest  season  of 
the  year  ;  for  the  holder  must  necessarily  be  out  of  action  for  some  weeks  during  the 
alterations.  Albeit,  many  undertakings  have  gone  through  this  ordeal  on  12  hours' 
storage,  even  when  based  on  the  minimum  day  (8-9  hours  of  maximum  day). 

The  proportions  of  gasholders  are  discussed  in  Chapter  XVII,  but  for  single  lift 
holders  allow  height  equal  to  0-3  to  04  of  the  diameter,  and  for  multiple  lift  holders 
0-6  to  1-0  of  the  diameter.  This  excludes  tanks  in  both  cases. 

TAB  AND  LIQUOR  STORAGE 

A  good  tar  storage  is  advisable,  as  it  assists  the  manager  in  times  of  low  prices, 
in  addition  to  which  the  sale  is  a  fluctuating  one. 

If  the  works  manufacture  its  own  sulphate,  it  is  advisable  not  to  store  am- 
moniacal  liquor  for  too  long,  owing  to  evaporation  and  other  losses.  A  general 
guide  is  5  weeks'  (maximum)  storage  for  tar  and  liquor. 

SULPHATE  PLANT 

Assuming  that  sulphate  is  made  ten  or  twelve  times  a  year,  the  plant  should 
have  a  capacity  of  3-3£  tons  of  sulphate  per  24  hours  for  every  million  cubic  feet 
of  gas  per  maximum  day.  This  allows  for  sulphate  making  during  six  days.  If 
it  is  proposed  to  make  at  different  periods,  or  for  more  or  less  days,  the  adjust- 
ments can  be  made  accordingly. 


MODERN   GASWORKS   PRACTICE 


WORKS  MAINS 

It  is  difficult  to  give  definite  rules,  but  the  following  will  form  a  rough  guide, 
based  on  particulars  of  many  works  : — 


Mains  5  inches  diameter  suitable  for  works  of 
6 


10 

12 

15 

18 

20-21 

24 

30 


3  to       4  million  cubic  feet  per  annum. 

6 

10        „,.... 

15 

25        „          , 

30 

45 

55 

90 

„ 

• 

100 

150 

M 

, 

- 

200 

300 

,, 

, 

_ 

350 

450 

,, 

, 

f 

500 

600 

, 

9 

600 

900 

,    • 

9 

GENERAL   NOTES   ON  THE   LAYING-OUT   OF   WORKS 

Having  decided  upon  the  sizes  of  buildings  and  plant,  the  engineer's  next  task 
is  that  of  setting  these  out  on  the  site  at  his  disposal.  Each  site  will  have  its  own 
particular  conditions,  but  the  following  points  may  be  taken  as  applicable  to  all 
circumstances. 

The  retort- house  and  coal  stores  should  be  adjacent  to  the  point  of  coal  intake; 
and,  in  laying-out,  the  disposal  of  coke  must  also  be  kept  in  mind.  If  possible, 
arrange  for  the  coal  storage  which  is  not  under  cover  to  be  also  convenient  for  the 
retort-house,  and  allow  plenty  of  room  for  coke  storage,  and  for  pulling  up  carts, 
etc.  High  coke  tips  should  be  avoided,  as  they  are  expensive  and  give  rise,  to  exces- 
sive quantities  of  breeze.  The  coal  and  coke  handling  should  be  quite  separate 
(on  opposite  sides  of  the  building,  if  possible)  ;  and,  if  the  site  is  not  being  filled  up 
at  once,  room  should  be  left  for  enlarging  without  undue  destruction.  Provision 
should  be  made  for  any  items  of  extension  which  may  be  contemplated.  The  site 
should  be  laid  out  for  what  it  is  comfortably  capable  of,  so  that  each  piece  of  plant 
may  have  room  for  extension  up  to  that  limit.  Cartage  ways  and  other  means  of 
access  must,  if  possible,  be  left  around  all  buildings. 

Boilers  should  be  central  for  feeding  exhausters,  mechanical  washers,  sulphate 
plant,  pumps,  etc.  ;  whereas  gasholders  should  be  kept  on  the  side  towards  the 
populated  parts,  thus  partly  shielding  the  works,  with  the  purifiers  and  sulphate 
plant  far  away  from  entrance  gates  and  roads.  Plenty  of  room  should  be  left  near 
the  purifiers  for  laying  out  oxide,  a  generous  portion  of  this  being  under  cover.  A 
point  which  is  often  overlooked  is  that  of  keeping  the  gasholders  as  far  as  possible 
from  the  causes  of  corrosion,  such  as  the  water-gas  plant,  chimneys,  sulphate 
plant,  etc.  ;  whilst  purifiers  should  be  some  distance  from  the  boiler  houses.  The 
ideal  place  for  scrubbing  plant,  in  fact  all  plant  for  the  extraction  of  tar  and  ammonia, 
is  next  to  the  storage  wells — thus  avoiding  long  distances  for  pumping.  It  is  scarcely 
necessary  to  add  the  warning  that  all  underground  tanks  should  be  kept  out  of 
the  line  of  heavy  traffic. 


PLANNING   AND   LAYING   OUT   OF   GASWORKS       19 


ESTIMATED    COST   FOR   A   500-MILLION   WORKS 

In  drawing  up  specifications  for  a  gasworks  of  some  definite  capacity  it  is 
invariably  the  practice  to  put  down  apparatus  of  a  sufficient  size  to  take  up 
future  requirements. 

In  the  following  estimate,  however,  this  has  not  been  done,  for  it  is  desired  to 
show  the  reasonable  cost  of  producing  and  distributing  about  500  million  cubic  feet 
per  annum — the  expenditure  on  a  works  having  its  apparatus  designed  with  a  view 
to  dealing  with  an  output  of  an  additional  20-40  per  cent,  cannot  be  taken  as 
exemplifying  the  minimum  outlay.  For  this  reason  the  figures  will  probably  be 
considered  by  some  as  being  on  the  low  side. 

It  is  assumed  that  about  20  per  cent,  of  carburetted  water  gas  will  be  made, 
on  the  average.  All  costs  include  foundations,  and  relate  to  the  normal  con- 
ditions prior  to  the  European  war. 


LAND  . 


HORIZONTAL 
RETORT  BENCH 
FOUNDATIONS, 
FLOORING,  ALL 
IRONWORK  AND 
ACCESSORIES 


1  acre  per  100  millions  per  annum, 
or  2  acres  per  million  per  diem.  5 
acres  at  £7CO 

Settings  of  "  tens  "  suitable,  20  feet 
retorts  (i.e.  five  tiers  of  two)  as 
occupying  least  ground  space. 
Assume  "  make  per  mouthpiece  " 
8,500  cubic  feet  per  diem,  machine 
charging. 

Required  make  (maximum  per  day) 

annual  make       _.      .,,.          ,. 
= —  —  =  2±  million  cubic 

220 

feet.  Less  20  per  cent,  for  water 
gas,  1,800,000  cubic  feet  of  coal  gas 
per  diem. 

Make  per  setting  8, 500x20  =  170,000 
cubic  feet.  No.  of  settings  re- 


.     ,  1,800,000 
quired  — - 


say  10  or  11. 


170,000 

In  addition  20  per  cent,  should  be 
allowed  for  retorts  "  scurfing  "  or 
otherwise  out  of  action,  bringing  the 
total  number  of  beds  up  to  13. 


3,500 


Canied  forward 


.     £3,500 


per 

mouth- 
piece. 


134 


13-4 


£ 

per  ton 

of  coal 

per  max. 

day. 


23-3 


23-3 


20 


MODERN   GASWORKS   PRACTICE 


per 

mouth- 
piece. 


£ 

per  ton 

of  coal 

per  max. 

day. 


RETORT  HOUSE 
AND  COAL 
STORE 


COAL  STORAGE 


Brought  forward 

Average  cost,  including  foundations 
and  accessories,  chimney,  etc.,  £50 
per  mouthpiece,  i.e.  260  x  50. 

Capacity  in  cubic  feet  required  for 
13  settings. 

Length. — Each  setting  9  feet  6  inches 
-f-  12J  per  cent,  for  passages,  out- 
side walls,  etc.  =  140  feet. 

Width. — Assume  projector  charging 
from  one  side  only. 


Width  of  bench 

Floor  space.     Charging  side.    . 
,,         ,,        Discharging  side 

Total 


ft. 
20 
23 
17 

60 


Three  weeks'  storage  under  cover. 
Max.  day's  coal  consumption 

1,8CO,CCO       lt»A 
=—  -  =150  tons. 

12,000 

Three  weeks'  storage  150  x  21  =3,150 
tons. 

Coal  will  occupy  3,150  x  42  =  132,3CO 
cubic  feet. 

Depth  must  not  exceed  20  feet,  pre- 
ferably 16  feet.  Length  of  house 
is  140  feet.  Then  required  width 
for  coal  store  (if  coal  stacked  16 
feet  deep)  to  give  this  capacity 
=  59  feet,  say  60  feet. 

Total  effective  width  of  house 

ft. 
=  60  -f  60  =  .  .  .  .  120 

Add  for  division  walls       .      .  2 


Total  internal  width 
Carried  forward   . 


122 


3,5CO 


13,CCO 


13-4     23-3 


£16,500 


50 


*86-7 


63-4 


110-0 


PLANNING   AND   LAYING   OUT   OF   GASWORKS       21 


per 

mouth- 
piece. 


£ 

per  ton 

of  coal 

per  max. 

day. 


COAL  ELEVATORS  . 


Brought  forward 


Height. — Dependent    upon    type    of 
house.     Stage  house  most  suitable. 

Height,  ground  level  to  ft.  in. 

working  stage   ...       .       96 

Height,  working  stage  to  top 

of  settings 15    0 

Height,  additional  headroom 
for  continuous  hoppers, 
coal  conveyors,  etc.  .  .  16  6 


Total  to  eaves  . 


41     0 


60 


Rise  of  roof  about  £  of  span  —  =  15 
feet. 

Internal  Capacity. — 140  feet  long  x 
122  feet  wide  x  48  feet  high  (this 
is  mean  height  of  building  to  half- 
way up  roof)  =  820,000  cubic  feet. 
Assume  a  steel-framed,  brick-panelled 
structure    at   2frf.   per   cubic  foot 
(including  foundations)  .... 
*Note. — Owing  to  the  excess  retort  capacity 
allowed,  the  figures    given    (£86-7    and 
£62 -7)  for  complete  cost  of  retort  house 
would  naturally  undergo  some  reduction 
if  full  carbonizing  capacity  was  made  use 
of. 

Breakers,  conveyors,  breaker  pits, 
overhead  hoppers,  coke  trucks, 
rails,  etc 

In  this  case  average  cost  per  mouth- 
piece for  above  would  be  £12. 

260  mouthpieces  at  £12    . 

N.B. — Coke  conveyors  would  be  in 
addition  to  this,  say  £3  to  £4  per 

Carried  forward 


16,500 


63-4 


110-0 


9,400 


3,120 


29,020 


36-2 


*62-7 


12-0       20-8 


111-6 


193-5 


22 


MODERN   GASWORKS   PRACTICE 


POWER  PLANT 


CONDENSERS  . 


EXHAUSTERS  . 


WASHER 
SCRUBBER 


TOWER 
SCRUBBERS 


Brought  forward 

foot,  or  an  additional  cost  of  £800 
to  £1,000,  according  to  length. 
Projector,  pusher,  trolley  wire,  cab- 
ling and  accessories 

Gas  engines,  dynamos  switchboard, 
cabling  and  all  accessories.  In  this 
case  average  cost  per  mouthpiece 
£5  to  £6  . 


daily  make 
22 


Max.  hourly  make  = 

1,800,000 
— • =  82,000  cubic  feet  per 

99 

hour. 

Two  water- tube  condensers  to  take 
40,000  to  50,000  cubic  feet  per  hour 
each,  fitted  complete  .... 

One  at  80,000-100,000  cubic  feet  per 
hour. 

Two  at  40,000  cubic  feet  per  hour. 

Engine  of  about  10  h.p.  required  for 
large  exhauster,  6  h.p.  for  smaller 
one.  (Note  that  this  plant  is  put 
down  in  duplicate)  ...  .*'-. 

Say  vertical  centrifugal  type  to 
take  80,000  to  90,000  cubic  feet  per 
hour.  Complete  with  engine  and 
bevel  gear  drive  .  .  ;  . 

Total  capacity  on  basis  of  6  cubic  feet 
per  1,000  cubic  feet  of  gas  per  diem. 
1,800  X  6  =  10,800  cubic  feet. 

Two  scrubbers  each  40  feet  high  by  14 
feet  diameter  would  be  suitable, 
thus  giving  6,000  cubic  feet  for  each 
vessel ;  an  allowance  10  per  cent, 
in  excess  of  the  minimum. 


29,020 


1,700 


1,430 


per 

mouth- 
piece. 


1,000 


1,100 


800 


1,900 


Carried  forward £36,950 


111-6 


6-5 


5-5 


4-2 


3-1 


7-3 


£ 

per  ton 

of  coal 

per  max. 

day. 


193-5 


114 


9-5 


142-0 


74 


5-3 


12-7 


246-5 


PLANNING  AND   LAYING   OUT   OF   GASWORKS       23 


DRY  PURIFICA- 
TION PLANT 


STATION  METER 


STORAGE 


GOVERNORS 


PUMPS 


Brought  forward     • 

Assume  that  oxide  only  is  to  be  used. 
Then  a  set  of  four  purifiers,  at  the 
minimum  allowance,  worked  in 
rotation,  with  two  small  catch 
boxes  would  suffice.  Area  required 
for  each  box  0-5  square  foot  per 
1,000  cubic  feet  per  diem.  1,800  x 0-5 
=900  square  feet,  i.e.  boxes  30 
feet  square  by  6  feet  deep. 

Size  of  connections  as  per  rule  on  later 
page  16,  v/9CO  —  4  =  30  less  4  = 
30—6  =  24  inches. 

Total  plant — complete  with  all  valves, 
lifting  gear,  etc 

To  pass  85,000-90,000  cubic  feet 
per  hour,  24  inch  connexions 

One  holder  (in  addition  to  water-gas 
relief  holder)  is  here  assumed,  al- 
though if  the  works  had  grown 
from  small  beginnings  there  would 
be  more.  As  the  works  has  a  water- 
gas  plant,  18  hours'  storage  should 
be  ample. 

Total  make  (water  gas  and  coal  gas) 
2J  million  cubic  feet  per  diem. 
18  hours'  storage  If  million  cubic 
feet. 

Telescopic  gasholder,  with  guide 
framing  and  tank  (brick  and 
puddle). 

Approximate  cost  £11  10s.  per  1,000 
cubic  feet  ....... 

Dependent  upon  system  of  distribu- 
tion employed,  but  assuming  three 
in  operation 

Liquor,  tar  and  water 

Carried  forward 


36,950 


4,6CO 
1,000 


20,000 

360 
250 


£63,160 


per 

mouth- 
piece. 


142-0 


17-7 
3-8 


76-9 

14 
1-0 


242-8 


£ 

per  ton 

of  coal 

per  max. 

day. 


246-5 


30-7 
6-7 


133-3 

2-4 
1-7 


421-3 


MODERN   GASWORKS   PRACTICE 


STEAM  BOILERS 


BUILDINGS 


TAR  AND  LIQUOR 
STORAGE. 


PAVING,  DRAIN- 
ING, FENCING 
&  INCIDENTALS 

SULPHATE  PLANT 


Brought  forward  .      .     '.'    , 

(Exclusive  of  water-gas  plant),  for 
driving  pumps,  exhausters,  sulphate 
plant,  etc. 

Two  required — one  as  a  stand-by, 
including  seatings  .  _. .  .;  ..  . 

(Other  than  retort  and  water-gas 
houses). 

Exhauster  House. — (Say)  20,CGO  cubic 
feet  capacity,  at  5d.  .... 

Meter  and  Governor  House. — Do. . 

Boiler  House. — 12,000  cubic  feet,  at 
4d.,  also  chimney  .  .  ..  .  . 

Generating  House,  Stokers'  Lobbies, 
etc. — 25, COO  cubic  feet,  at  5d. . 

Steel -framed  purifying  shed  to  cover 
purifiers  and  preparing  floor,  11,500 
square  feet  area,  at  Is.  6rf.  .  . 

One  or  more  wells  brick -rendered. 
Minimum  capacity  5  weeks,  maxi- 
mum make  of  tar  and  liquor 
(say)  225,000  gallons,  then  capa- 
city required  36,000  cubic  feet, 
i.e.  well  60  feet  X  50  feet  x  12 
feet  deep,  divided  into  two  or  more 
sections, 

Average  cost  per  cubic  foot  =  8d.   . 


(Exclusive  of  steam  boilers),  with 
purifiers  for  waste  gases.  Approxi- 
mate make  475  tons  per  annum, 
or  (say)  6J  tons  per  day  working 
72  days  per  year  .  .  .  . 

Building  for  above  plant.  30,000 
cubic  feet,  at  Qd.  per  cubic  foot 

Carried  forward   .      .      . 


63,160 


1,200 

420 
420 

300 
520 

860 


£ 

per  ton 

I  of  coal 
mouth- 

per  max. 


1,300 


1,200 
750 


£71,330 


piece. 


242-8 


1-6 
1-6 

1-2 
2-0 


5-0 


day. 


421-3 


4-6  :      8-0 


20 
•o 

2-8 
2-0 
3-5 


3-3         5-7 


1,200  !       4-6         8-0 


8-7 


4-6         8-0 
2-9         5-0 


274-2 


475-8 


PLANNING   AND   LAYING   OUT   OF   GASWORKS       25 


VAEIOUS 


MAINS  (Steam, 
water  and  gas 
connexions) 


Brought  forward 

i.e.  Tools,  carts,  weighbridge,  and 
other  appurtenances.  . 

Offices,  laboratory,  manager's  or  fore- 
man's house,  furniture  and  equip- 
ment. Stores  

On  works  only 


Total  expenditure  on  works  (less 
water-gas  apparatus) 

From  the  above  it  is  seen  that  the 
complete  equipment  of  a  works  of 
this  size  entails  an  expenditure  of 
over  £3CO  per  mouthpiece,  and 
about  £540  per  ton  of  coal  car- 
bonized per  maximum  day.  This, 
of  course,  is  exclusive  of  expendi- 
ture on  water-gas  plant.  The  cost 
per  1,CCO  cubic  feet  per  maximum 
diem  would  be  £45. 


£ 

£ 

per 
mouth- 
piece. 

per  ton 
of  coal 
per  max. 
day. 

71,330 

274-2 

475-8 

1,000 

3-8 

6-7 

6,000 

23-1 

40-0 

3,000 

11-5 

20-0 

£81,330 

312-6 

542-5 

CARBURETTED   WATER-GAS    PLANT 

Make  per  day  20  per  cent,  of  total  make  =  450,000  cubic  feet.  £ 

Plant  in  two  sections,  each  250,000  cubic  feet  capacity  per  diem.     Complete 
with  generators,  carburettors,  superheaters,  scrubbers,  condensers,  and 
operating  floor ;    also  blowers  and  engines  for  same,  tar  well,  coke  lift, 
pumps,  etc.        ...;.......      4,000 

Boilers  and  seatings  for  above       .  •      •*.          .          .          *         .          .          .         950 
Exhausters  (in  duplicate),  25,000  cubic  feet  per  hour,  with  engines    .          .         450 
Purifiers  for  oxide  of  iron  only,  20  feet  x  20  feet  x  5  feet  deep,  complete 

with  connexions  and  lifting  gear         .......      2,000 

Building  for  water-gas  apparatus,  65^000  cubic  feet,  at  5d.  to  5Jd          .      1,450 
Shed  for  purifiers,  with  preparing  floor  to  cover  6,000  square  feet,  at  Is.  6d.         450 
Oil-storage  tank.    Thirty- six  days'  consumption  at2J  gallons  per  1,000  cubic 
feet  of  gas  made,  45,000  gallons,  complete  with  fittings      .          .          .         350 


Carried  forward 


£9,650 


26 


MODERN   GASWORKS   PRACTICE 


Brought  forward 

Meter  to  pass  25,000  cubic  feet  per  hour       ..... 
Relief  holder,  30,000  cubic  feet  capacity,  at  £42  per  1,000  cubic  feet 
Gas,  tar,  steam  and  water  connexions  ...... 


£ 
9,650 

400 
1,260 

250 


Total  cost  of  complete  water-gas  plant,  i.e.  £23  per  1,000  cubic  feet  per  max. 

diem .-.         .  £11,560 

(N.B. — For  a  comparatively  small  outlay,  one  section  could  be  increased  to 

300,000  cubic  feet  per  diem.) 
Cost  of  coal-gas  plant.  .        ..,,.-.         ...         »  .       -         •         •    81,330 


Total  cost  of  works        .         .       •.."'.       '  . •     '   . 

Cost  per  million  cubic  feet  made  per  annum   .         '. 
*  Cost  per  million  cubic  feet  sold  per  annum  . 
Cost  per  1,000  cubic  feet  made  per  max.  diem 

*  Estimated  at  480  million  cubic  feet. 


£92,890 


£186 

£194 

£41  10*. 


DISTRIBUTION 

Without  knowing  the  general  outlines  of  the  district  and  the  system  of  distri- 
bution to  be  adopted,  whether  high-pressure  mains  will  be  run  in  addition  to  low- 
pressure,  or  whether  "  boosting  "  will  be  necessary,  it  is  difficult  to  give  anything 
more  than  an  approximate  figure  under  this  item.  The  following,  however,  may 
be  taken  as  typical,  and  generally  conforming  to  the  case  in  question. 


MAINS      .     . 

SERVICES  . 

METERS   .     .     .     .. 

COOKERS,  FIRES,  ETC. 


About  1 10  miles  ;  these  would  vary  from  about 
24  inches  for  trunk  mains  to  4  inches  for  the 
smaller  offshoots .  . . 

To  supply  6,5CO  "  ordinary  "  and  8,500  "  slot  " 
consumers,  also  for  industrial  purposes  . 

"  Ordinary,"  6,500,  including  fixing,  at  £2  each. 

Prepayment  iristallations,  8,5CO  at  £5  each, 
inclusive  of  cooker,  3  fittings,  piping,  etc.  . 

For  "  ordinary  "  consumers  (including  fixing) 
(say)  3,500 

Total  cost  of  distribution  equipment    . 


65,000 

17,000 

13,000 

42,500 
12,500 


£150,000 


N.B. — Columns  and  lamps  for  public  lighting  are  usually  the  property  of  the 
local  authority  ;  but,  if  rented  from  the  gas  company,  the  cost  to  the  latter  would 
be  about  £4  10s.  per  lamp  complete,  including  column,  lantern,  and  service.  In  the 
above  instance  from  1,200  to  1,400  would  be  required,  entailing  an  additional  expen- 
diture of  about  £5,500. 


PLANNING   AND   LAYING   OUT  OF  GASWORKS       27 

SUMMARY 


Percentages  of 
total  outlay. 


Total  cost  of  works 

Total  cost  of  distribution 

Engineering  and  contingencies,  10  per  cent. 
Law  and  Parliamentary  charges,  2£  per  cent. 


92,890 

34-0 

150,OCO 

55-0 

24,000 

8-8 

6,000 

2-2 

£272,890 


100-0 


Capital  expended  per  million  cubic  feet  made  per  annum     .          .     £546 
Capital  expended  per  million  cubic  feet  sold  ,,  .  £570 

Capital  expended  per  thousand  cubic  feet  made  per  max.  day         .     £120 
The  foregoing  estimate  has  been  set  out  more  or  less  in  detail  in  order  to  show 
the  methods  employed  for  arriving  at  the  approximate  expenditure  entailed  in  the 
erection  of  a  comparatively  large  works.     In  order,  however,  that  this  book  may 
be  of  assistance  in  the  case  of  estimating  for  small  works,  it  has  been  thought  advis- 
able to  include  figures  giving  expenditure  which  may  be  taken  as  typical  for,  first, 
a  50-million,  and  secondly,  a  15-million  concern.     The  items  given  are  taken  from 
actual  figures  for  works  recently  erected  and  now  in  operation,  and  the  costs  are 
tabulated  in  such  a  manner  as  to  show  the  difference  in  every  item  of  expenditure. 
The  figures  given  for  Works  "  A  "  concern  an  undertaking  selling  50  million 
cubic  feet   per  annum  in  a  semi-country   district,  with   small  mining  and  other 
industries,  and  a  population  of  from  14,000  to  15,000. 
The  sale  of  gas  is  made  up  as  follows  : — 

1,5CO  prepayment  consumers  at  12,OCO  cubic  feet     18  mills,  per  annum. 

9CO  ordinary  consumers  at  33,000  cubic  feet      .30        „  ,, 

Public  lighting    .         .         .         .         .         .  2        ,,  „ 

50  millions. 


The  figures  for  Works  "  B  "  are  for  the  15-million  undertaking,  made  up  of 
three  small  towns  in  a  partly  rural  and  partly  residential  district.  The  sales  are 
accounted  for  as  follows  : — 

500  prepayment  consumers  at  11,000  cubic  feet    5-5  mills,  per  annum. 
300  ordinary  consumers  at  32,CCO  cubic  feet     .     9-6       ,,  ,, 

Public  lighting          .         ...          .          .     0-5       ,,  ,, 

15-6  millions. 

In  the  latter  case  it  will  be  noted  that  the  length  and  cost  of  mains  is  excessive, 
Bowing  to  the  linking-up  of  townships  by  a  large  proportion  of  unproductive  main. 
-All  costs  include  connexions  and  foundations  complete. 


MODERN   GASWORKS   PRACTICE 
COSTS   OF   WORKS   AND   DISTRIBUTING   PLANT 


"A" 
50  millions. 


"B" 

15  millions. 


£  £ 

Land:  "A,"  f  acre;  "B,"  1  acre    .      ......  5CO  300 

Fencing,  paving,  and  draining      .      .      .         ..      .     .     .  160  100 

Retort  house  and  coal  store 1,7CO  720 

Retort  settings,  floorings,  chimney,  accessories  ("B  "  has 

very  small  margin)     .      .      .      .     ,      .      ...      .      .  2,550  780 

•Condenser       ........    ^      .'...,.•...  150  60 

Exhausters  ("A"  in  duplicate),  also  engines  .      ...  350  120 

Coal  truckway  for  feeding  store   .      .....      ...  240 

Scrubber   .     .     ...     .     .     .•    .     ....     ...     .     .  355  150 

Livesey  washer ICO 

Purifiers  and  oxide  shed  and  traveller  complete  ("A"   of 

ample  size,  "  B  "  slightly  deficient)     .      .      .....  1,110  400 

Station  meter .     .     .      .      ...  380  100 

Holder  (one  in  each  case) .      •  5,280  2,060 

Governor  (one  in  each  case)    ....>.,..  HO  45 

Boilers  (in  duplicate),  seating,  and  chimney      .      .      .     .  730 

Tar  and  liquor  storage .      .      .  •  .     ",".  370  75 

Buildings,  stores,  etc .      .     .      .      .      .  650  340 

iSmall-  pumps,  tanks,  tools,  etc.     .      .      ....      .      .      .  180  100 

Works'  connexions  (small  for  "A,"  extensive  for  "  B  ")    .  220  170 

Weighbridge 65 

15,2CO  5,520 

Engineering  and  contingencies      .      .      .     .     .      .      .      .  1,CCO  130 

Total  wo  Its'  costs    ......     .'•'.''.-.    '.     .     .  £16,210  5,650 

Mains:  "A,"  18  miles;  "B,"  10  miles  ......  9,8CO  5,200 

.Services,  ordinary  and  slot 2,450  830 

Meters,  ordinary,  including  fixing 1,750  610 

..Stoves  and  fires,  ordinary  consumers  (and  fixing)   .      .      .  1,450  4CO 
Prepayment    installations,   complete,   including    3  points, 

3-lt.  or  5-lt.  meter,  and  cooker  or  griller  .      .      .      .      .  6,750  2,380 

22,200  9,420 

Engineering  and  contingencies 600  90 

Total  distribution  costs £22,800  9,510 


PLANNING   AND   LAYING   OUT   OF   GASWORKS       29 


"A" 
50  millions. 

"B  " 

15  millions. 

£ 
16,200 

22,8CO 
2,CCO 

£ 
5,650 
9,510 
610 

Total  capital  outlay      

£41,CCO 

15,770 

324 

470 
40 

360 
606 
39 

Parliamentary    .... 
Total        •      

£834  ' 

£1,005 

CHAPTER  II 
FOUNDATIONS,    GASWORKS'    BUILDINGS,    ETC. 

EMPHASIS  has  already  been  laid  upon  the  advisability  of  securing  a  gasworks'  site 
which  is  of  low- level  in  comparison  with  the  major  portion  of  the  district  to  be  supplied. 
The  works,  however,  will  not  necessarily  be  erected  on  the  lowest-lying  portion,  as 
it  may  give  rise  to  trouble  in  connexion  with  water  or  bad  foundations.  Certainly, 
money  may  usually  be  saved  in  the  first  instance ;  but  unsuitable,  spongy  subsoils 
are  almost  invariably  associated  with  land  of  this  description,  and  untold  damage 
may  afterwards  be  occasioned  by  abnormal  flooding.  Nevertheless,  in  some  cases 
other  attractions  may  more  than  balance  the  prospect  of  an  excessive  expenditure 
on  foundations,  and  gasworks  have  before  now  been  erected  on  land  reclaimed  from 
the  sea.  Accordingly,  the  choice  of  the  site  must  not  be  influenced  by  consideration 
of  the  immediate  saving,  and  the  various  factors  require  to  be  carefully  balanced 
before  any  hasty  decision  is  come  to. 

Before  a  site  is  definitely  purchased,  trial  borings  must  be  sunk,  so  that  a  fair 
indication  of  the  substrata  may  be  obtained.  On  an  extensive  site  one  such  boring 
is  by  no  means  sufficient,  as  comparatively  abrupt  changes  in  the  character  of  the 
strata  are  frequently  found.  The  more  general  practice  is  to  sink  a  circular  boring 
about  four  feet  in  diameter,  the  sides  of  the  excavation  being  shuttered  up  by  means 
of  a  light  wooden  casing  as  the  digging  advances.  The  casings  are  usually  worked 
in  about  6-feet  lengths.  A  less  costly  and  laborious  method  consists  in  driving 
down  a  special  boring  auger,  which  brings  the  core  to  the  surface  as  it  proceeds, 
thus  enabling  an  accurate  knowledge  of  the  character  of  the  subsoil  to  be  ob- 
tained. An  auger,  complete  with  the  necessary  boring  outfit,  is  shown  in  Fig.  1. 
The  first  step  is  to  sink  a  shallow  pit  3  or  4  feet  deep  by  about  4  feet  square,  and 
to  shutter  this  up  with  timber.  The  shear-legs  is  then  erected  over  the  centre  of 
the  pit,  and  the  boring  rope  is  connected  to  the  end  of  a  special  joint  rod,  to  the 
other  end  of  which  the  auger  itself  is  attached.  The  auger  is  then  drilled  into  the 
earth  by  a  twisting  motion,  and  periodically  withdrawn  by  means  of  the  wind- 
lass for  the  removal  of  the  strata.  The  sketch  shows  a  "  clay  "  auger  in  use. 
It  is  found  that  with  normal  soils  of  the  clay  and  soft  gravel  type  a  core  of  strata 
about  3  feet  in  length  may  be  brought  up  at  each  operation.  In  the  event  of  the 
soil  proving  extremely  hard,  and  of  a  rocky  nature,  a  special  tool  of  a  chisel  type 
is  employed,  and  the  strata  broken  up  by  a  series  of  blows.  Strata  drills  of  this 
kind  may  be  used  for  boring  shafts  of  from  4  inches  to  2  feet  in  diameter ;  for 

30 


FOUNDATIONS,   GASWORKS'   BUILDINGS,   ETC.        31 

most  purposes  the  smaller  holes  will  give 
ample  indication  of  the  nature  of  the  ground. 
The  4-inch  boring  is,  however,  not  to  be 
advised ;  and  for  the  majority  of  sites 
the  8-inch  drill— as  stipulated  by  the 
London  County  Council — is  certainly  to  be 
recommended.  Having  once  bored  the 
hole,  observations  of  the  rise  and  fall  of 
water  must  be  made.  These  should  ex- 
tend over  some  period,  and  may  usually 
be  carried  out  merely  by  dipping  at  fairly 
frequent  intervals,  particular  attention 
being  given  to  the  effect  of  heavy  rain- 
storms, or  other  causes  likely  to  influence 
the  water  level.  Trial  boreholes  must  on 
all  occasions  be  taken  lower  than  the  pro- 
bable depth  of  the  foundations,  so  as  to 
remove  all  doubt  as  to  the  character  of  the 
proposed  bed ;  whilst  strata  of  a  gravelly 
nature  should  be  regarded  with  suspicion,  in 
that  they  may  eventually  prove  to  be  inter- 
spersed with  seams  of  running  sand. 

Before  the  excavation  proper  for 
foundations  is  commenced  steps  must  be 
taken  for  the  adequate  control  of  all  sur- 
face and  sub-surface  water  ;  in  fact  it  may  ' 
in  abnormal  cases  be  found  profitable  to  lay 
down  a  drainage  system  which  is  capable  of 
dealing  with  water  to  a  depth  somewhat 
below  that  of  the  proposed  excavations. 
This  procedure  is,  however,  decidedly 
costly,  and  should  only  be  countenanced 
in  extreme  instances. 

FOUNDATIONS 

When  the  depth  of  an  excavation  ex- 
ceeds a  few  feet,  some  method  of  timbering 
must  usually  be  employed,  whilst  when  the 
depth  is  greater  than  10  feet,  considerable 
precaution  is  necessary,  so  much  so  that 
the  Board  of  Trade  prescribe  that  in 
such  cases  an  expert  shall  be  called  in. 

The    excavation    of    ground    for    gasholder    FlG-  1. -STRATA  DRILL  IN  OPERATION  FITTED 
.  °  .  WITH  BORING  AUGER  TO  RECOVER  SUBSOIL 

tanks   calls  for  particular  care  and   expen-          IN  LENGTHS  OF  3  FEET  6  INCHES. 


32 


MODERN   GASWORKS   PRACTICE 


ence.  In  general,  foundations  are  classed  under  the  two  headings  of  "  natural  '* 
and  "  artificial,"  according  as  to  whether  the  ground  requires  special  treatment 
other  than  shallow  excavation.  In  this  country  the  four  most  common  subscils. 
to  be  met  with  are  (a)  ordinary  earthy  material,  (b)  hard  and  soft  clay,  (c)  gravel, 
and  (d)  chalk ;  and  it  is  the  compressible  soils  of  the  soft  clay  and  earthy  types 
which  demand  the  greatest  amount  of  attention. 

It  may  be  said  that  as  a  general  rule  (particularly  where  foundations  for  retort 
benches  are  concerned)  it  will  be  profitable  to  put  down  a  solid  block  of  concrete, 
so  long  as  the  total  depth  does  not  exceed  5  feet.  Beyond  this  the  procedure 
becomes  expensive,  and  one  of  the  various  "  artificial  "  methods  should  be  resorted 
to.  The  cost  of  excavation  will,  of  course,  largely  depend  upon  the  material  which 
is  being  taken  out ;  but  if  a  good  ganger  is  in  charge,  he  will  often  find  some  means- 
of  selling  the  debris,  or  of  getting  it  carted  "away  by  a  local  contractor  free  of  charge. 
When  the  conditions  of  the  substrata  necessitate  a  comparatively  deep  foundation, 
or  when  the  soil  is  more  or  less  compressible,  the  following  methods  may  be 
employed  : — 

(a)  Concrete  piers. 

(6)  Floating  foundation. 

(c)  Piles,  either  wood,  metal,  or  reinforced  concrete. 


Stable  Ground 
FIG.  2. — PIER  FOUNDATION. 


Particulars  of  the,  pier  methods  are  shown  in  Fig.  2,  from  which  it  will  be  seen 
that  the  complete  area  is  first  excavated  to  a  depth  of  a  few  feet,  whilst  at  inter- 

. vals  shafts  are  sunk  through  the  soft  soil  on 

j  .  \          to  the  stable  ground.     The  dimensions  *  of 

(  (          these    shafts    vary    with    the    purpose    for 

which  the  foundation  is  required,  but  they 
will  usually  run  about  2  feet  in  width,  and 
extend  laterally  the  entire  breadth  of  the 
foundation.  For  buildings,  etc.,  the  piers 
may  be  so  much  as  from  20  to  25  feet  apart, 
rough  arches  being  thrown  from  pier  to  pier 
by  digging  out  the  ground,  so  as  to  form  a 
centering.  When  dealing  with  retort  bench  foundations  it  is  usual  to  drop  down 
a  pier  beneath  each  supporting  wall  of  the  main  setting-arches ;  hence  in  such 
cases  the  piers  are  pitched  at  about  8  to  10  feet  centres.  When  the  subsoil 
necessitates  sinking  to  a  greater  depth  than  12  feet,  it  is  advisable  to  discard 
the  pier  method,  and  to  drive  down  reinforced  concrete  piles,  which  may  be  em- 
ployed in  the  form  of  continuous  piers,  or  spaced  at  equal  distances  apart.  In  the 
latter  case  the  stability  of  the  upper  slab  should  be  ensured  by  running  some  type 
of  reinforcement,  such  as  old  railway  metals,  from  head  to  head  of  the  piles,  or  by 
introducing  one  of  the  many  systems  of  special  bars  or  metal.  In  fact,  any  method 
may  be  employed  which  has  the  effect  of  forming  a  continuous  slab  by  binding  the 
heads  of  the  piles  together,  thus  ensuring  equal  loading. 

To-day,  the  favourite  method  of  dealing  with  average  compressible  soil  is  by  means 


Main  Col.umn 
Supporting  Bench 


FOUNDATIONS,   GASWORKS'   BUILDINGS,   ETC.       33 

of  some  type  of  floating  foundation  in  the  form  of  a  raft,  often  with  stiffening  ribs 
as  in  a  large  ceiling.  That  is  to  say,  the  weight  of  the  superstructure  is  distributed 
over  a  large  area,  so  that  the  unit  loading  on  the  soil  is  within  the  recognized  limit. 
In  such  cases  the  distribution  of  loading  must  be  as  equal  as  possible  ;  otherwise,  if 
sinking  occurs,  the  whole  may  go  slightly  out  of  level.  In  this  respect  it  must  be 
remembered  that  it  is  frequently  impossible  to  avoid  a  little  sinking ;  but  unequal 
sinking  is  the  great  danger.  The  once  familiar  type  of  grillage  foundation,  embrac- 
ing an  elaborate  network  of  joists  bolted  together,  is  now  giving  way  to  reinforced 
concrete  work,  this  having  proved  to  be  the  most  economical  form  of  foundation 
which  can  be  employed  under  any  circumstances.  An  alternative  but  more  ex- 
pensive method  is  that  of  employing  one  of  the  many  forms  of  metal  sheet  piling, 
thus  completely  enclosing  the  space  to  be  built  over.  A  very  light  raft  spread 
over  the  enclosed  area  will  then  suffice.  This  is  certainly  an  admirable  way  of  deal- 
ing with  soils  of  a  spongy  character.  As  an  illustration  of  its  efficacy,  it  may  be 
mentioned  that  in  America  buildings  have  been  erected  on  what  has  practically 
amounted  to  a  body  of  water,  the  latter,  being  incompressible,  affording  an  ideal 
support  so  long  as  lateral  movement  is  effectively  restrained. 

Some  few  years  ago  it 
was  a  common  practice  to 
set  down  raft  foundations 
constructed  from  timbers  tied 
together,  also  from  fascines  ; 
but  such  methods  may  now 
be  looked  upon  as  things  of 
the  past.  As  an  example  of 
the  modern  slab  foundation, 
an  illustration  of  a  method 
adopted  for  the  erection  of 
a  vertical  retort  bench  and 
house  is  shown  in  Fig.  3.  Fig.  4  shows  such  a  foundation  with  the  reinforcement 
in  position  before  the  concrete  is  inserted.  Here  the  slab  is  of  a  more  or  less  shallow 
nature,  but  is  heavily  reinforced  by  means  of  indented  bars.  The  disposition  of  the 
bars  is  such  that  they  are  called  upon  to  relieve  the  concrete  of  the  greater  part  of 
the  tensional  and  shear  stresses.  In  the  case  shown  the  foundation  was  required  to 
support  several  rows  of  columns,  each  carrying  a  load  of  approximately  90  tons ; 
accordingly  the  maximum  reinforcement  occurred  in  open  squares  in  alignment 
with  the  columns,  whilst  the  remaining  portions  of  the  slab  were  provided  with 
considerably  less  reinforcement.  When  foundations  of  the  floating  type  are  em- 
ployed on  the  more  easily  compressible  soils  care  is  necessary  to  see  that  no  derange- 
ment takes  place,  otherwise  adjacent  buildings  may  suffer  disturbance.  Founda- 
tions, to-day,  however,  are  not  of  the  massive  character  employed  in  the  past,  owing 
to  the  tendency  to  erect  light  steel-framed  buildings  with  a  comparatively  thin 
filling. 


Slab  18  Deep 
I 


w'r.^^jzr~  : ~  v>  •  '^>^^r\™ 

I " :>  ^-^- TN  V 7*t   * .?  J  *j  I  **  f?*FttJ '- :r  *vi  t 


\  |  Bars  at  15  Centres 

FIG.    3. — TYPICAL    REINFORCED    RAFT    FOUNDATION    FOR 
VERTICAL  RETORT  BENCH. 


i) 


MODERN   GASWORKS   PRACTICE 


FIG.  4. — REINFORCED  RAFT  FOUNDATION  FOE  VERTICAL  RETORT  BENCH,  SHOWING  INDENTED 
BARS  IN  POSITION  BEFORE  CONCRETING- UP. 


ALLOWABLE  PRESSUKES  ON  VARIOUS  SOILS 


gravel  (firm)  with  underlying  chalk 
Firm  gravel   .         v         .      .  ..... 

Firm  clay       .          .         .'         . 
Gravel  (loose)  and  sand  .     '    . 

Light  earth  and  sandy  loam  . 
Made-up  ground  (well  rammed) 


6     to  7  tons  per  square  foot. 

5      „    6      „  „ 

3      ,,4      „  ,. 
If   ,,    2^ 

I ',',  4  "  ',! 


"When  slabs  of  concrete  for  retort  benches  are  laid  down  on  any  type  of  clay 
it  will  be  found  profitable  to  drop  a  layer  of  fine  sand  (from  3  inches  to  6  inches 
'deep)  on  to  the  surface  of  the  clay  before  filling  in  with  concrete.  Concrete,  being 
of  a  homogeneous  nature,  readily  conducts  heat,  so  that  in  time  the  moisture  is 
-dried  up  from  the  clay,  with  the  result  that  shrinkage  occurs,  and  the  whole  may 
be  thrown  out  of  level.  The  strength  of  the  concrete  is  a  question  to  which  due 
thought  must  be  given,  and  this  particularly  applies  to  gasworks  undertaking 
extensions,  where  there  is  usually  a  stock  of  "  hard-core  "  on  hand.  The  gas  engineer 
is  very  prone  to  get  rid  of  his  old  broken  retorts  on  such  occasions,  and  in  many 
instances  there  is  little  reason  why  these  should  not  be  used  in  moderation.  It 
must  be  remembered,  however,  that  the  modern  highly  porous  retort  has  a  low 
crushing  strength,  and  in  view  of  this  fact  it  is  best  excluded  from  the  more  impor- 
tant work.  Cement  concrete  is  nearly  always  used  nowadays  in  preference  to  the 
lime  variety,  owing  to  its  greater  strength,  and  should  seldom  be  mixed  in  higher 
ratios  than  1  to  6,  unless  the  ground  is  good,  in  which  case  a  mixture  of  1  to  8  or  9 
may  be  safely  used.  The  aggregate  is  best  composed  of  a  fairly  coarse  ballast,  or 
hard  bricks  broken  to  a  size  not  exceeding  2  inches,  with  an  adequate  proportion 
of  sand.  Care  must  be  taken  to  see  thai  all  mortar  adhering  to  the  bricks  is  removed. 
Concrete  .mixers  .are  .a  present-day  fashion,  but  except  for  extensive  building  opera- 


FOUNDATIONS,    GASWORKS'   BUILDINGS,   ETC.        35 

tions  in  reinforced  work  it  is  questionable  whether  they  effect  any  marked  economy. 
Many  authorities  are  of  the  opinion  that  the  hand-mixed  material  is  far  superior. 

It  is  difficult  to  lay  down  any  hard  and  fast  rule  for  the  cost  of  foundations, 
but  in  the  case  of  the  ordinary  rectangular  slab  an  average  figure  would  be  13s.  £d. 
to  16s.  6d.  per  cubic  yard  complete,  including  excavation  to  a  depth  not  exceeding 
4  feet. 

Excavation  only  varies  from  IQd.  to  Is.  6d.  per'cubic  yard  up  to  a  depth  of 
4  feet ;  beyond  this  depth  it  will  be  from  Is.  6d.  to  2s.  6d.,  which  includes  light 
timbering. 

MODERN   GASWORKS   BUILDINGS 

Engineers  in  the  past  have  not  neglected  to  add  an  artistic  touch  to  the  archi- 
tecture of  the  gasworks,  and  evidence  of  this  is  seen  in  the  cast-iron  embellish- 


FIG.  5. — STEEL-FRAMED  AND  44  INCH  BRICK-PANELLED  RETORT  HOUSE. 


ments,  finials,  etc.,  introduced  for  the  supposed  beautification  of  certain  plant 
and  buildings.  It  would  appear,  however,  that  the  tendency  of  the  present  age 
is  in  the  direction  of  utility  alone,  it  being  realized  that  under  no  circumstances  can 
a  gasworks  be  represented  as  ornamental ;  hence  simplicity  of  design  has  commenced 
to  assert  itself  at  every  turn.  So  far  as  the  general  style  of  buildings  is  concerned, 
economy  goes  hand-in-hand  with  simplicity  of  outline  ;  accordingly  these  two  must 
rank  as  primary  considerations.  Other  factors  bearing  on  the  ultimate  decision 
are : — 

(a)  Wear  and  tear,  the  cost  of  maintenance,  re-painting,  etc. 

(b)  The  choice  of  materials  suited  to  the  purpose  for  which  the  building  is 


36 


MODERN   GASWORKS   PRACTICE 


FIG.  6. — EXPANDED  METAL. 


required,  e.g.  in  corrosive  atmospheres 
material  such  as  corrugated  iron  should 
be  dispensed  with. 

(c)  Adaptability    for   future  exten- 
sions   without    the    necessity    for   con- 
siderable destruction. 

(d)  Ample  provision  for  the  recep- 
tion and  dispatch   of  materials  in  con- 
nection with   the   operation    for   which 
the  building  is   required.     In   the  case 
of    engine  houses,  large  entrance  doors 
should  be  provided,  so  that  the  instal- 
ment of  larger  plant  in  the  future  will 

not  necessitate  cutting  through  walls. 

(e)  The  buildings  should  be  roomy,  and  of  ample  height,  with  efficient  means 
for   ensuring   ventila- 
tion. 

(/)  There  must 
be  an  abundance  of 
light. 

(g)  The  prevail- 
ing conditions  should 
be  easy  and  con- 
genial for  the  men, 
facilities  being 
afforded  for  keeping 
themselves  and  their 
apparatus  in  a  state 
of  cleanliness. 

In  the  past  it 
has  been  an  almost 
universal  custom  to 
erect  such  buildings 
as  retort  houses  of 
substantial  dimen- 
sions in  brickwork, 
although  later  the 

steel- framed  structure  entirely  sheeted  with  corrugated  iron  found  a  certain  amount 

of  favour  in  small  works.  Both  methods, 
however,  have  their  disadvantages.  The 
first  is  excellent  once  it  is  erected,  but  the 
capital  expenditure  is  excessive,  being  as 
much  as  4rf.  per  cubic  foot,  inclusive  of  roof 
FIG.  8.— HY-RIB  METAL  an(^  foundations.  Corrugated  ironwork, 


FIG. 


7. — WATER-GAS  HOUSE  IN  STEEL  FRAMEWORK,  EXPANDED  METAL, 
AND  CONCRETE  PLASTERING.     SOLID  WALLS  3  INCHES  THICK. 


FOUNDATIONS,   GASWORKS'   BUILDINGS,    ETC.        37 

on  the  other  hand,  is  economical  when  considered  in  the  light  of  first  cost,  but  is  a 
never-ending  expense  so  far  as  maintenance  and  painting  is  concerned.  In  any 
case,  if  a  corrugated  structure  is  decided  upon,  it  should  be  understood  that  in  no 
circumstances  should  the  sheets  be  brought  down  to  ground  level.  A  dwarf 
concrete  wall,  about  a  foot  to  18  inches  in  height,  should  be  provided,  the  sheets 


FIG.  9.— INTERIOR  VIEW  OF  HY-RIB  WALL  AFTER  ONE  COAT  OF  PLASTER  ON 

OUTSIDE. 

being  brought  down  to  the  top  of  this.  During  recent  years  there  has  been  a  grow- 
ing  tendency  to  dispense  with  both  corrugated  iron  and  massive  brickwork,  and 
the  light  steel-framed  house  panelled  with  thin  brickwork  is  making  considerable 
headway  in  this  country.  An  illustration  of  this  type  of  building,  which  can  be 
effectively  used  for  retort  house,  engine  house,  and  all  classes  of  buildings,  is  shown 


38 


MODERN  GASWORKS  PRACTICE 


in  Fig.  5,  where  the  brickwork  is  4£  inches  thick.    The  approximate  cost,  including 
foundations  and  roofing,  is  2|rf.  to  3d.  per  cubic  foot  of  content. 

Another  very  cheap  method  of  construction  is  that  \vhich  introduces  patent 
metal  meshings,  such  as  expanded  metal  or  "  Hy^rib."  Retort  houses  and  other 
buildings  built  up  with  the  aid  of  such  material  are  primarily  provided  with  a  steel 
frame,  as  in  the  case  of  the  brick-panelled  house,  but  the  open  squares  between  the 
main  framing  are  filled  in  with  the  metal  meshing,  and  the  whole  is  then  given  a 
plaster  coating.  Examples  of  expanded  metal- work  are  given  in  Figs.  6  and  7,  whilst 
the  "  Hy-rib  "  is  seen  in  Figs.  8,  9  and  10.  The  plaster  is  usually  composed  of  3 
parts  of  Portland  cement  to  11  or  12  parts  of  sand,  and  the  total  thickness  of  the 

side  walls 
varies  from  If 
inches  to  3 
inches,  in  ac- 
cordance with 
the  spacing  of 
the  supports. 
The  approxi- 
mate cost  of  a 
building  o  n 
the  "Hy- 
rib  "  principle 
amounts  to  an 
average  of  Id. 
to  2fd.  per 
cubic  foot 
of  contents, 
which  includes 
foundations, 
sashes,  glaz- 
ing, doors,  or 
roller  shutters. 

For  vertical  retort  houses  this  type  of  structure  has  proved  particularly  suitable,  this 
being  largely  due  to  the  fact  that  the  vertical  house  may  be  built  far  more  lightly 
than  that  for  horizontal  retorts,  owing  to  there  being  no  heavy  floors  to  support ;  but 
it  is  not  to  be  recommended  for  buildings  having  an  excessive  number  of  sashes, 
openings,  etc.,  as  the  extra  cost  of  providing  framing  for  these  is  appreciable. 

COMPARATIVE  COSTS  or  VARIOUS  BUILDINGS 

Massive  brickwork,  old  type,  slated  roof       .     3|rf.  to    4d.  per  cubic  foot  contents. 
Entire  brickwork  (modern),  slated  roof          .     2%d.    ,,    3^d.    „         „         „       „       „ 
Steel  frame,  corrugated  sheeting  throughout      2d.      „    2%d.    „         ,,         ,,       „       ,, 
Steel  frame,  brick  panelling,  slated  roof        .     2^d.    „    3d.      „         „         „       „       „ 
Steel  frame,  trussed  patent  metal  and  plas- 
tered, slated  roof  .          .          .          .     2d.      „    2%d.    „         „         „       „      „ 
(All  complete  with  foundations.) 


FIG.  10. — A  VERTICAL  RETORT  HOUSE  IN  Hy-Ris  AND  CONCRETE  FILLING. 


FOUNDATIONS,   GASWORKS'   BUILDINGS,   ETC.       39 

In  the  case  of  the  last-mentioned  item,  the  expenditure  would  be  made  up 
approximately  as  follows  : — 

Foundations         .          .          .          .  Q-lOd. 

Building      ....'...  .  1'oOd. 

Roofing       .  .  Q'55d. 

2~15d.  per  cubic  foot. 

With  the  concrete  structure  much  depends,  of  course,  on  the  comparative 
cost  of  bricks  and  ballast  on  the  site.  If  the  latter  can  be  dug  from,  the  subsoil 
the  concrete  building  is  inapproachable  on  grounds  of  economy.  In  one  instance- 
a  building  of  this  type  was  recently  erected  for  rather  less  than  Ifrf.  per  cubic  foot.. 
The  total  capacity  amounted  to  750,000  cubic  feet,  the  foundations  were  6  to  8  feet 
deep,  and  the  concrete  forming  the  sides  was  shuttered  up  to  a  height  of  24  feet, 
the  remaining  10  feet  to  the  eaves  being  composed  of  moulded  concrete  blocks.  In* 
this  case  ballast  was  obtainable  from  the  site,  and  the  major  part  of  the  founda- 
tions were  composed  of  3  parts  of  coke  breeze,  3  parts  of  clinker,  3  parts  of  washed 
ballast,  and  1  part-of  cement.  The  filling  material  and  concrete  blocks  were  made 
up  of  7  to  8  to  1  concrete,  3  parts  of  this  being  ballast.  In  structures  of  this  type 
care  should  be  taken  to  ensure  that  clinker  or  breeze  in  the  concrete  does  not  come 
into  actual  contact  with  the  steelwork. 

So  far  as  retort- house  construction  is  concerned,  a  usual  rough  rule  for  arriving: 
at  an  approximate  cost  for  a  brick-panelled  or  brick  and  concrete  house  per  mouth- 
piece to  be  installed  is  the  following : — 

For  stage  house          .......     £24  to  £  48  per  mouthpiece.. 

For  subway  house     .......     £22    ,,    £12     ,,  „ 

These  prices  include  merely  the  house  and  coal  store,  and  no  machinery,  retort- 
bench  work  or  flooring.  They  allow,  however,  for  foundations.  The  lower  margin 
.given  applies  to  the  larger  houses  of  (say)  more  than  150  mouthpieces.  For  a 
medium-sized  stage  house  take  £26  to  £35  per  mouthpiece. 

THE   DESIGN   OF   COAL   STORES 

Although  the  brick- panelled  or  plastered-steel  structure  admirably  serves  the 
purpose  of  affording  a  covering  to  the  retort-bench,  the  whole  question  requires 
somewhat  serious  consideration  when  the  storage  of  coal  is  concerned.  Thin  plaster, 
or  4-|  inch  brickwork  walls  are  in  no  sense  capable  of  withstanding  for  long  the  lateral 
thrusts  of  a  deep  coal  heap,  and  although  cases  are  known  where  such  buildings 
are  being  used  for  the  purpose  without  visible  detriment,  there  is  little  doubt  that 
the  factor  of  safety  is  extremely  low,  and  considerable  risks  must  be  run.  For  all 
this,  there  is  no  reason  why  the  light  concrete  house  should  not  be  employed  for 
storage  purposes,  so  long  as  those  portions  acting  as  retaining  walls  are  effectively 
reinforced  on  the  inner  or  tension  side.  A  good  plan  is  to  employ  old  railway 
metals,  these  being  rigidly  interlaced  with  piping  or  iron  rods  of  about  |-inch  to 
1-inch  diameter.  In  the  light  panelled  buildings  the  steel  framing  must  be  closer 


40  MODERN   GASWORKS   PRACTICE 

and  stronger,  whilst  a  thin  wall  can  be  made  of  many  of  the  patent  reinforcements  on 
"the  market. 

If  large  coal-stocks  are  to  be  regularly  maintained  under  cover  it  cannot  be 
disputed  that  the  entire  brick  building,  panelled  and  buttressed,  provides  the  best 
form  of  shelter.  Formerly  these  structures  were  erected  almost  without  exception, 
'and  the  fact  that  they  are  still  doing  duty  as  both  coal  stores  and  houses  to-day 
'speaks  well  for  their  design  and  durability  ;  and  the  same  may  be  said  of  thick  con- 
crete or  stone  walls.  If  perfect  reliance  is  to  be  felt,  it  is  essential  that  the  walls 
of  coal  stores  should  be  designed  on  scientific  lines,  and  the  pressures  due  to  the 
coal  carefully  computed.  For  this  purpose  the  well-known  Rankine  formula  for 
earth  pressures  may  be  employed,  and  the  wall  will  be  sufficiently  stable  if  the  middle- 
third  condition  is  neglected,  and  the  resultant  pressure  cuts  the  various  sections 
within  the  width  of  the  base  at  any  one  section.  In  working  out  the  pressure  the 
weight  of  ordinary  bituminous  coal  may  be  taken  as  54  Ib.  per  cubic  foot,  and  the 
angle  of  repose  as  45°.  Then  the  formula  is  :  — 

_W/;2/l  —Sin   <p\ 
~2M+Sin~V 

Where     P  =  total  pressure  per  foot  run  at  a  depth  of  h  feet. 
W  =  weight  of  coal  per  cubic  foot  =  54  Ib. 
<p  =  the  angle  of  repose  of  coal  =  45°. 

For  instance,  suppose  it  is  required  to  find  the  thickness  of  walls  necessary  for 
stacking  coal  to  a  depth  of  15  feet.    Then— 


P  = 


_ 

I  -}-  Sin  45  / 


;=    Ix 


From  this,  P  is  found  to  be  1,042  Ib.  at  a  depth  of  15  feet,  or  an  average  pressure 
of  69  Ib.  per  square  foot.  This  gives  the  total  horizontal  pressure  at  the  bottom 
of  the  wall,  and  from  the  triangle  of  forces  the  position  of  the  resultant  may  be 
found,  and,  accordingly,  the  thickness  of  the  wall  at  the  base.  If  the  same  treat- 
ment is  applied  to  find  the  pressure  at  various  depths,  the  allowable  decrease  in 
thickness  as  the  wall  rises  is  obtained. 

In  cases  where  the  wall  simply  serves  as  a  retaining  wall,  so  that  coal  can  be 
surcharged  above  it,  the  formula  must  be  used  in  the  following  somewhat  compli- 
cated form,  viz.  :  — 

(Cos 
V 


Cos  7  +  A/Cos  2  7  —  Cos  2  <p 

where  y  is  the  angle  of  surcharge. 

This,  however,  reduces  itself  to  a  simple  and  easily  workable  form  when  the 
angle  of  surcharge  is  equal  to  the  angle  of  repose  of  the  coal,  as  would  nearly  always 
be  the  case.  The  formula  then  becomes  :  — 


n 

P  =  --  Cos  9 


FOUNDATIONS,    GASWORKS'   BUILDINGS,   ETC.        41 

The  above  treatment,  of  course,  applies  to  the  stacking  of  broken  or  small  coal. 
"When  the  coal  itself  is  formed  into  a  wall  (as  commonly  seen  in  railway  yards),  a 
reduced  wall-thickness  may  be  taken. 

When  the  erection  of  coal  stores  is  contemplated,  the  question  of  chief  impor- 
tance is  as  to  whether  the  projected  floor-level  is  of  sufficient  height  to  escape  ground 
water  after  a  heavy  rainfall,  also  its  relation  to  the  level  of  the  retort -house  working 
.stage.  The  floor  should  preferably  be  paved  with  slabs  of  stone  or  concrete,  and 
designed  so  that  moisture  can  drain  away.  In  this  respect  the  design  in  Fig.  12 
is  to  be  preferred  to  that  shown  in  Fig.  11.  The  practice  is  often  followed  of  dividing 


FIG.  11.  FIG.  12. 

the  store  into  separate  bins  by  means  of  vertical  cross- walls,  and  this  is  certainly  of 
advantage  in  preventing  a  fire  from  spreading.  Moreover,  each  of  these  bins  can 
be  made  of  a  definite  capacity  (so  many  tons  per  foot  deep),  which  enables  a  good 
idea  of  the  stock  to  be  obtained  at  a  glance.  Iron  columns  and  ties  passing  through 
bins  should  be  avoided  as  far  as  possible,  as  they  are  said  to  favour  the  spread  of 
fire — in  any  case  they  should  be  coated  with  concrete.  Plenty  of  fresh  air  in  the 
covered  store  is  an  important  item,  for  men  suffer  from  the  ill-effects  of  a  poorly 
ventilated  building.  This  is  supposed  to  be  due  to  the  vapours  of  acetaldehyde, 
which  are  known  to  interfere  with  respiration.  Ventilation  is  best  provided  for  by 
a  continuous  louvre  running  along  the  roof  of  the  store,  or  by  large  openings  made 
above  the  level  at  which  it  is  proposed  to  stack  coal. 

TYPES  OF  RETORT  HOUSES 

There  are  two  standard  types  of  retort  houses  to  be  found  in  use  at  the  present 
day,  whilst  a  third  but  less  common  structure  is  also  met  with  at  some  works. 
These  are  :— 

(a)  Stage  houses. 

(b)  Subway  houses. 

(c)  Intermediate   type.     A   combination    of    (a)    and    (b). 
Included  under  (a)  are  all  those  houses  in  which  the  clinkering-floor  is  on  the 

ground-level,  whilst  the  charging-floor  is  elevated.  The  modern  vertical  retort 
house,  although  differing  from  the  horizontal  type  in  many  respects,  would  also 
come  under  this  heading.  The  former  houses  are  invariably  of  greater  height  than 
the  latter,  averaging  (for  the  25-foot  retorts)  about  52  feet  to  the  eaves,  whilst 
horizontal  houses  are  seldom  more  than  40  feet.  "  Vertical  "  houses,  moreover,  can 
be  made  of  fairly  light  design,  as — unlike  the  house  for  "  horizontals  " — they  have 


42  MODERN   GASWORKS   PRACTICE 

only  to  support  themselves,  and  to  withstand  the  wind  pressure  to  which  they  may 
be  subjected.  In  the  subway  house  the  charging-floor  is  on  a  level  with  the  mean 
ground-level,  the  ground  being  excavated  so  that  producers,  slides,  etc.,  are  all  below. 
The  intermediate  type  is  seldom  met  with,  and  includes  all  those  houses  which  have 
the  charging-floor  partly  above  ground-level  and  the  clinkering-floor  below  it.  The 
existence  of  a  subway  house  may  in  many  instances  be  accounted  for  by  the  fact 
that  a  works  originally  started  in  a  more  or  less  small  way  with  direct  fired  settings 
—in  which  case  a  single  floor  is  sufficient,  this  being  at  ground-level.  As  business 
increased  it  may  have  been  decided  to  adopt  some  more  efficient  type  of  firing, 
which,  owing  to  the  increased  room  required  in  order  to  ensure  a  deeper  fuel  bed, 
means  either  raising  the  roof  or  excavating,  the  latter  course  very  frequently  being 
preferred.  Before  making  a  decision,  however,  great  care  is  necessary  to  see  that 
the  surface  of  the  proposed  foundation  will  not  be  below  the  high-water  level.  In 
any  case  it  is  preferable  to  enclose  the  whole  of  the  subway  with  an  impervious 
sheeting.  This  may  be  done  by  lining  the  sides  with  concrete,  backed  with  puddle, 
or  with  rendered  brickwork ;  but  preferably  by  building  twin  walls  and  filling  in 
the  intervening  space  with  pitch. 

In  spite  of  the  increased  expenditure  entailed  with  the  stage  house,  it  is  almost 
without  exception  the  favourite  for  modern  retort-house  work.  The  conditions 
under  which  men  are  called  upon  to  do  their  work  receive  far  greater  attention 
than  in  the  past,  and  it  is  generally  recognized  that  the  intense  heat  of  the  majority 
of  subways,  with  the  escaping  steam  arising  from  quenched  coke  or  clinker,  and  the 
inability  to  adequately  ventilate  the  subways,  is  anything  but  conducive  to  the  honest 
performance  of  duty.  On  the  other  hand,  the  stage  house  can  be  effectively  venti- 
lated, coke  quenching  is  facilitated,  and  steam  can  be  quickly  got  rid  of.  The  coke, 
moreover,  can  be  wheeled  out  direct  into  carts,  this  also  applying  to  ashes  and  clinker. 
In  the  case  of  the  subway  house,  some  means  has  to  be  provided  for  bringing  the 
ashes  (and  in  many  cases  the  whole  of  the  coke)  to  ground-level. 

So  far  as  the  intake  of  coal  is  concerned,  the  subway  house  will  in  some  instances 
hold  the  advantage,  in  that  the  coal  when  deposited  in  the  store  is  at  charging-level. 
With  the  medium  and  larger  sized  houses  this  cannot,  however,  be  said  to  be  of 
great  importance,  owing  to  the  common  use  of  some  form  of  coal-handling  plant. 
With  small  houses,  where  hand- charging  is  in  vogue,  the  point  is  of  some  importance. 

The  distance  between  the  upper  and  lower  floor-levels  varies  from  5  to  10  feet, 
the  former  being  the  allowance  in  very  small  subway  houses  ;  but  if  adequate  depth 
is  to  be  given  to  the  producer,  the  height  should  not  be  less  than  8  feet.  As  regards 
this,  it  will  be  seen  from  Fig.  13  that  in  the  stage  house  the  difference  between  the 
floor- levels  accounts  for  a  certain  bulk  of  coal  which  has  to  be  brought  to  the  working 
tage.  This  increases  the  cost  of  handling,  unless  the  store  is  fitted  with  elevators 
for  feeding  overhead  hoppers.  This  is  not  the  case  with  the  arrangement  shown 
in  Fig.  14. 

A  point  which  has  accounted  for  a  good  deal  of  discussion  is  the  effect  of  the 
type  of  house  on  the  air  supply  to  the  producers.  Some  authorities  have  objection 
to  the  stage  type  owing  to  its  tendency  to  set  up  draughts  that  may  influence  the 


FOUNDATIONS,    GASWORKS'   BUILDINGS,   ETC.        43 

composition  of  the  furnace  gases.     On  the  other  hand,  it  is   said  that  a  freer  air 
supply  is  obtained,  therefore  more  regular  working  of  the  producers. 

As  a  general  rule,  however,  it  will  be  found  that  water  is  the  deciding  factor, 


rround  Level 


FIG.  13. — STAGE  HOUSE. 


FIG.  14. — SUBWAY  HOUSE. 


and  if  this  is  found  near  the  surface,  a  stage  house  should  forthwith  be  decided  upon. 

Concerning  relative  costs,  it  may  be  taken  that  the  stage  house  costs  anything 
from  £2  to  £6  more  per  mouthpiece  than  the  subway  type  costs. 

In  smaller  works  the  subwray  may  be  left  entirely  uncovered,  and  the  retorts 


FIG.  15. — TRAVELLING  FLOOR  FOR  SUBWAY  RETORT  HOUSE. 


operated  from  a  travelling  platform  running  on  ball-bearings,  and  readily  operated 
by  hand.  In  such  cases  the  precaution  must  be  taken  of  railing  off  the  subway, 
•unless  this  is  provided  for  by  a  running  cable  as  shown  in  Fig.  15. 


44 


MODERN   GASWORKS   PRACTICE 


RETORT-HOUSE   ROOFS 

The  use  of  timber  for  the  construction  of  principals  must  be  avoided  in  retort 
houses.  The  building  for  horizontal  benches  is  usually  provided  with  an  all-steel 
trass  ;  the  well-known  "  English  "  or  "  French  "  types  made  up  of  all-rolled  sections 
:are  effective  and  economical.  Slates  are  the  most  general  covering,  although  many 
forms  of  patent  compressed  asbestos  sheets  and  tiles,  costing  about  25  per  cent, 
less  than  slates,  have  recently  been  introduced  with  success.  Owing  to  somewhat 
heavy  deterioration  due  to  corrosion,  steel  used  in  retort-house  roofs  and  other 
work  should  not  be  highly  stressed,  and  a  factor  of  safety  of  7  on  the  breaking  strength 
.should  be  allowed  for,  i.e.  a  stress  not  exceeding  4|  tons  per  square  inch  in  tension 
.or  compression. 

RETORT-HOUSE   FLOORS 

Except  in  connexion  with  the  smaller  works  the  stage  house  will  usually  be 
•decided  upon,  as  the  many  contingent  advantages  will  be  found  to  neutralize  the 
additional  first  cost  entailed.  For  small  works,  where  any  stoking  apparatus  is  in 
use  (such  as  the  manual  type),  the  floor,  whether  at  ground-level  or  above  it,  is  fre- 
quently composed  of  f-inch  or  J-inch  chequer  plates,  bolted  down  to  cross  joists. 
.For  the  larger  works,  where  heavy  machines  giv  ng  rise  to  high  rolling  loads  have 

Concrete  or 
Brick  Paving 

Concrete  Filling 


TYPE  A 


Expanded  Metal 
or  Hy.-Rib 


R.S.J 


TYPE  B 


R.S.J. 


Method  of  Protecting 
Underside  of  R.S.J. 


Expanded  Metal  Strip 


/  Expanded  Metal 
May  be  Inserted  Here 


Concrete  Filling 
V 


Paving  Tiles,  Concrete 
or  Blue  Bricks  on  Edge 
/  Steel  Troughing 


J I       I  _\J        \S.  I 


R.S.J. 


R.S.J. 


TYPE  C  TYPE  D 

FIG.  16.— TYPES  OF  RETORT-HOUSE  FLOORS. 


lo  be  allowed  for,  additional  strength  is  necessary,  and  wear  and  tear  on  a  chequer- 
plate  floor  is  considerable.  Several  types  of  retort-house  floors  are  shown  in  Fig.  16, 
and  within  recent  years  a  tendency  has  developed  to  employ  some  system  of 
reinforced  concrete  as  shown.  A  serviceable  method  of  building  the  concrete  arches 
is  that  of  fixing  in  sheets  of  thin  metal  or  corrugated  iron,  these  being  left  in  after 
the  work  is  finished. 

A  point  requiring  attention  is  that  of  allowing  ample  room  for  expansion  of 
joists  composing  the  floor ;   otherwise,  when  expansion  of  the  bench  and  joists 


FOUNDATIONS,   GASWORKS'   BUILDINGS,   ETC.      45 

sets  in  serious  stressing  may  result  in  the  ultimate  yielding  of  some  portion  of  the 
structure.  It  is  certainly  preferable  to  arrange  for  independent  columns  some 
inches  from  the  buck-stays,  the  main  floor  girders  being  carried  on  these,  so  that 
the  whole  floor  is  completely  independent  of  the  bench. 

Owing  to  the  continued  quenching  of  coke,  the  clinkering  of  fires,  etc.,  the 
under  portion  of  the  steelwork  where  exposed  is  particularly  liable  to  corrosion. 
An  effective  method  of  preventing  this  fs  to  cover  the  lower  webs  of  the  joists  with 
cement,  which  may  be  made  to  cling  permanently  by  attaching  a  strip  of  expanded 
metal  as  shown  in  type  C,  Fig.  16. 

The  variation  in  size  of  retort-house  floors  makes  it  difficult  to  lay  down  more 
than  approximate  figures  for  their  cost.  In  the  main,  however,  the  following  may 
be  looked  upon  as  average  examples  : — 

Stage  floor.  Chequer  plates  on  single  joists      .  2s.  3d.  to  2s.  6d.  per  square  foot. 

„         ,,  Double  joists,  concrete  arches       .  3s.  3d.  „    4s.  „         ,,          „ 

,,         ,,  Single  joist,  trough  and  concrete  .  3s.  9d.  „    4s.  6d.     „         „         „ 

„         „  For  charging  side,  heavy  machine  .  4s.  Qd.  „    5s.  3d.     „         „          „ 

As  the  wear  upon  gasworks'  floors  is  somewhat  considerable,  it  is  advisable 
to  avoid  breeze  and  clinker  in  the  concrete  used  for  the  floors.  Where  there  is 
a  thickness  greater  than  3J  inches,  the  best  material  will  be  made  from  4  parts  of 
aggregate,  2  parts  of  sand,  and  1  part  of  Portland  cement.  If  the  stresses  on  the 
floor  are  computed,  the  concrete  should  be  neglected  and  merely  regarded  as  filling, 
whilst  in  the  case  of  large  retort-house  floors  the  machine  loaded  to  its  maximum 
should  be  dealt  with  as  a  rolling  load.  The  weight,  furthermore,  must  be  assumed 
to  act  on  three  wheels  only,  this  often  being  the  temporary  condition  of  affairs,  due 
to  a  faulty  rail,  or  to  some  external  influence.  The  centre  columns  (see  Fig.  13) 
usually  associated  with  these  heavy  floors  must  be  strong  enough  to  take  the 
rolling  load  and  any  eccentricity  of  loading  which  may  be  caused  by  the  above- 
mentioned  factors. 


CHAPTER   III 
THE    HORIZONTAL    RETORT    BENCH 

THE  practice  of  laying  retorts  horizontally  is  still  the  most  common  in  this  country. 
In  spite  of  the  perfection  to  which  other  types  of  carbonizing  plant  has  been 
brought,  the  older  method  is  as  yet  able  to  hold  its  own,  and  there  is  little  fear  that 
it  will  be  universally  supplanted.  So  far  as  the  smaller  works  are  concerned,  the 
horizontal  bench  is  more  convenient,  and  less  costly  in  the  first  place  ;  and,  up  to 
the  present,  vertical  installations  have  been  chiefly  confined  to  those  works  where 
comparatively  large  quantities  of  coal  can  be  handled  with  a  considerable  saving 
in  working  expenses. 

There  are  three  types  of  horizontal  settings  in  common  use  to-day.     These  are  : 

1.  Direct-fired  settings. 

2.  Semi-gaseous  settings. 

3.  Gaseous-fired  settings. 

Types  2  and  3,  which  are  gradually  taking  the  place  of  the  more  extrava- 
gant direct-fired  settings,  may  again  be  subdivided  as  follows  :— 

(a)  Generator  settings. 

(6)  Regenerator  settings. 

(c)  Outside  producers  of  various  types. 

Although  the  initial  cost  of  the  gaseous-fired  setting  is  greater  than  that  of  the 
direct-fired  setting,  the  additional  outlay  is  soon  redeemed  by  the  saving  effected  in 
fuel.  For  this  reason  even  small  works  are  finding  it  profitable  to  instal  at  least 
the  generator  principle,  and  it  may  be  said  in  general  that  the  direct  system  should 
be  confined  to  those  works  making  less  than  2  or  3  million  cubic  feet  per  annum. 
In  such  cases,  interest  on  additional  capital  and  extra  labour  entailed  in  supervision 
make  the  gaseous  system  a  doubtful  advantage.  In  the  "  direct "  furnace  the  air 
passes  through  the  coke  in  large  and  often  unrestricted  quantities,  and  com- 
bines with  the  carbon  to  form  CO  2  directly.  In  the  gaseous  settings  the  retorts  are 
heated  by  the  exothermic  reaction  of  the  combination  of  CO  and  oxygen  in  forming 
C02.  The  great  drawback  to  the  direct  furnace  is  the  difficulty  of  controlling  the 
air  supply,  which  results  in  a  considerably  increased  consumption  of  fuel,  together 
with  irregular  heating  of  the  setting.  In  fact,  in  very  small  works,  where  the  plant 
is  not  making  gas  throughout  the  whole  twTenty-four  hours,  cases  have  been  known 
where  all  the  coke  has  been  made  use  of  for  heating  the  retorts,  and  in  isolated 

46 


THE  HORIZONTAL  RETORT  BENCH       47 

instances  an  additional  quantity  of  fuel  has  had  to  be  purchased  from  outside. 
About  double  the  quantity  of  air  enters  the  furnace  than  is  theoretically  neces- 
sary, which  has  the  effect  of  retarding  combustion  and  reducing  the  limit  of  tem- 
perature. This  is  chiefly  due  to  the. large  volumes  of  nitrogen  introduced  with  the 
air,  and  the  defect  has  been  overcome  in  some  measure  by  employing  the  semi- 
gaseous  system. 

The  quantity  of  fuel  necessary  for  the  carbonization  of  coal  has,  by  the  curtail- 
ment of  thermal  losses  in  every  direction,  been  reduced  to  such  fine  limits  that  at  the 
present  day,  under  ideal  conditions,  the  coke  required  is  only  about  11  per  cent, 
of  the  original  weight  of  coal.  The  fuel  consumed  under  the  various  systems  is 
normally  as  follows  : — 

Direct-fired  furnace          ...  40  per  cent,  of  coke  made  used  as  fuel. 

Generator  furnace  .          .      '   .          .  22  to  26  „  „  ,,  ,, 

Regenerator  furnace         .          .          .  16   ,,    20  ,,  ,,  ,,  ,, 

Vert' col  retorts — 

(a)  Intermittent  type  ...  23  ,,  ,,  ,,  „ 

(b)  Continuous  type     .          .          .  16J,,    18J 

Outside  producers  ....      18J ,,    23  ,,  ,,  ,,  „ 

In  giving  figures  such  as  the  above  the  basis  of  coke  made  per  ton  of  coal  car- 
bonized on  which  the  figures  have  been  calculated  must  always  be  stated.  In  the 
present  instance  the  yield  has  been  taken  as  14  cwts.  per  ton.  It  is  owing  to  the 
widely  varying  yields  of  coke  from  coals  that  this  method  of  gauging  fuel  results  is 
somewhat  unsatisfactory,  and  the  most  reliable  basis  is  that  of  "  Ibs.  of  fuel  used  per 
100  Ib.  of  coal  carbonized,"  such  as  given  in  the  table  below.  Chief  importance, 
however,  attaches  to  the  coke  actually  sold  per  ton  of  coal,  and  so  long  as  this  amounts 
to  10  cwts.  the  economy  of  the  system  of  firing  is  above  question. 

Direct-fired  furnace        ...  28  per  cent,  of  original  weight  of  coal  carbonized 

used  as  fuel. 

Generator  furnace  .          .          .15  to  18  ,,  ,,  ,,  „  ,, 

Regenerator  furnace        .          .  11    „    14  ,,  ,,  ,,  ,,  ,, 

Vertical  retorts — 

(a)  Intermittent  type  .          .  16  ,,  ,,  ,,  „  ,, 

(b)  Continuous  type    ...  11£         ,,  „  .,  ,,  ,, 
Outside  producers           .          .               13  „    16           ,,                 „             ,,             „             ,, 

The  low  fuel  figures  for  the  continuous  vertical  system  are  chiefly  accounted 
for  by  the  fact  that  the  heat  is  extracted  from  the  coke  before  it  leaves  the  retort, 
and  is  utilized  for  heating  up  either  the  primary  or  secondary  air  before  combustion. 
It  must  be  pointed  out,  however,  that  fuel  figures  for  verticals  are  at  present  more  or 
less  in  the  nature  of  experiments,  as  there  has  as  yet  been  little  opportunity  of  making 
comparisons  over  prolonged  periods. 

THEORY   OF   COMBUSTION 

An  elementary  scientific  fact  which  must  be  realized  at  the  outset  is  that  a 
definite  amount  of  coke,  whether  burnt  at  once  to  CO  2  in  the  direct  fire,  or  in  two 


48  MODERN   GASWORKS    PRACTICE 

stages,  as   in   the    gaseous    furnace,    in    each   instance  yields   a   similar   number 
of  heat  units.     This  may  be  simply  illustrated  as  follows  : — 

(1)  1  lb.  of  carbon  burnt  direct  to  CO2  evolves      .          .          .  14,550  B.Th.U. 

(2)  1  lb.  of  carbon  burnt  to  CO  evolves         ....  4,350         „ 
1  lb.  of  CO  burnt  to  CO2  evolves 4,371 

1st  stage.     1  lb.  of  carbon — 

C  +  i  (O2)  =  CO 

1  lb.  C  =  2-333  lb.  CO    =    4,350  B.Th.U. 
2nd  stage.         .  2-333  lb.  CO  =  2-333  x  4,371  =  10,200 

Total     14,550 


From  the  above  it  will  be  seen  that  the  greater  efficiency  of  the  gaseous  principle 
is  not  due  to  the  fact  that-  an  increased  number  of  heat  units  are  expelled  ;  the 
reason  is  that  the  heat  is  obtained  in  that  portion  of  the  setting  where  it  is  most 
useful,  and  the  bulk  of  gases  resulting  from  total  combustion  is  reduced  to  the 
smallest  practicable  limits.  It  is  not  proposed  to  deal  here  with  the  calculation  of 
combustion  temperatures,  as  the  procedure  is  explained  in  most  textbooks  on 
physics,  and  is  of  little  practical  use  to  the  gas  engineer. 

The  ultimate  limiting  temperature  is  influenced — 

(a)  By  the  calorific  power  of  the  fuel. 

(6)  By  the  total  weight  of  the  products  of  combustion  and  their  specific  heat. 

(c)  By  the  temperature  of  the  mixture  before  combustion. 

Of  these,  the  first  is  under  control  to  only  a  limited  extent,  as  the  fuel  used — 
coke — has  to  be  taken  as  it  comes,  the  calorific  power  depending  upon  the  type  of 
coal  carbonized  at  the  time.  It  is  largely  by  working  on  conditions  (6)  and  (c)  that 
the  increased  firing  efficiency  of  the  present  day  has  been  obtained.  With  regard 
to  the  total  weight  o£  the  products,  it  will  be  seen  that  the  greater  the  quantity  of  air 
admitted  to  the  furnace  for  the  combustion  of  a  definite  amount  of  fuel  the  greater 
will  be  the  weight  of  the  waste  products  over  which  a  fixed  number  of  heat  units 
will  be  spread.  Hence,  the  ideal  condition  is  that  of  admitting  just  sufficient  air 
for  combustion,  and  reducing  the  weights  of  the  waste  products  to  a  minimum — 
in  which  case  the  heat  units  are  concentrated  in  the  smallest  possible  volume  and  a 
maximum  temperature  is  obtained. 

When  pure  carbon  is  completely  burnt  with  no  more  or  less  than  the  requisite- 
quantity  of  air,  a  temperature  of  3,700°  Fahr.  is  theoretically  obtainable ;  but  if 
the  air  is  in  excess  to  the  extent  of  25  per  cent.,  the  temperature  is  forthwith  reduced 
to  3,540°  Fahr.  In  the  same  way,  if  air  is  deficient,  so  that  CO  alone  is  formed,  then 
the  temperature  attained  will  be  only  2,330°  Fahr.  If  pure  carbon  is  burnt  in  pure 
oxygen,  the  resulting  temperature  is  approximately  12,000°  Fahr.  The  effect  of  the- 
total  weight  of  products  on  the  ultimate  temperature  is  best  seen  from  the  following  :— 

1  lb.  of  carbon   burnt  in  pure  oxygen  requires  2-67  lb.  of  O2,  and  gives  3-67  lb.  of  waste 
products. 

1  lb.  of  carbon  burnt  in  air  requires  11-61  lb.  of  air,  and  gives  12-61  lb.  of  waste  products. 

The  increased  weight  in  the  second  instance  accounts,  in  the  main,  for  a  tem- 
perature reduction  of  8,300°  Fahr. 


THE  HORIZONTAL  RETORT  BENCH        49 

It  will  be  as  well  to  explain  here  the  meaning  of  the  term  "  Calorific  Intensity," 
which  must  on  no  account  be  confused  with  calorific  power,  from  which  it  differs. 
Calorific  intensity  is  measured  in  degrees  Fahrenheit  or  Centigrade,  and  is  the  maxi- 
mum temperature  theoretically  attainable  under  the  conditions  of  combustion 
prevailing  ;  hence  it  depends  very  largely  upon  the  way  in  which  the  fuel  is  employed. 

Producer  gas  resulting  from  the  combustion  of  coke  should  theoretically  consist 
of  34-8  per  cent,  of  carbon  monoxide  and  65-2  per  cent,  of  nitrogen,  by  volume.  In 
practice,  however,  ideal  conditions  are  not  to  be  looked  for,  and  the  ordinary  in- 
dividual retort-bench  producer  is  considered  to  be  giving  satisfactory  results  when 
the  carbon  monoxide  content  of  the  gas  averages  25  per  cent.,  the  carbon  dioxide 
amounting  to  about  5  per  cent.  The  modern  combustion  chamber  temperature 
rarely,  if  ever,  exceeds  2,800°  Fahr.,  and  under  normal  working  conditions  is  usually 
found  in  the  neighbourhood  of  2,500°  Fahr.,  with  an  actual  retort  temperature  of 
1,900°  to  2,000°  Fahr.  Several  causes  account  for  the  reduced  intensity,  among 
them  being  the  variations  in  the  depth  of  fuel  bed,  the  effect  of  clinker  on  the 
velocity  of  travel  of  the  gases,  and  the  various  sources  of  thermal  losses. 

The  actual  temperature  of  the  fire  is  of  some  importance  ;  and  whilst  the  recog- 
nized gasworks  rule  is  that  of  keeping  the  fuel-bed  cool,  this  axiom  can  be  carried 
too  far,  for  the  maximum  proportion  of  carbon  monoxide  is  reached  at  a  fuel-bed 
temperature  of  about  1,4CO°-1,5CO°  Fahr.  The  prevailing  temperature  is  from 
1,800°-1,900°  Fahr. 

Producer  gas  from  retort  furnaces  seldom  consists  of  merely  CO,  C02J  and  nitro- 
gen ;  for,  owing  to  steam  from  the  ashpan,  also  to  the  impossibility  of  ensuring 
the  entire  "  burning-off  "  of  all  coke  charged  from  the  retort  into  the  furnace,  a 
certain  quantity  of  hydrogen  and  methane  is  invariably  present.  The  following, 
in  fact,  is  the  average  composition  under  good  conditions  : — 

Carbon  monoxide    .          .          ..'•'».-       .        •.          .          .25  per  cent,  by  volume. 

Carbon  dioxide        .          »   •  .  . .       ..       5  „  „ 

Hydrogen       .  ......       6  „  „ 

Methane          .........       1  „  „ 

Nitrogen         «          ...          .          .          ;          ...     63  „  „ 

With  regard  to  the  regulation  of  the  weight  of  the  combustion  products,  the  gaa 
engineer  keeps  the  weight  to  a  minimum  by  manipulation  of  the  furnace  dampers  in 
conjunction  with  analyses  of  the  waste  gases.  In  order  to  allow  for  variation  in  the 
composition  of  the  producer  gas  no  attempt  is  made  to  admit  the  exact  quantity  of 
air  required  ;  but  the  waste  of  fuel  is  curtailed  by  ensuring  a  slight  excess  of  air — 
in  other  words,  by  admitting  sufficient  air  until  oxygen  is  present  in  the  waste  flue 
gases.  The  absence  of  oxygen  in  these  gases  is  a  fairly  sure  indication  of  the  presence 
of  carbon  mojioxide — the  latter  being  a  useful  combustible  product,  and  accounting 
for  the  blue  flame  so  frequently  to  be  seen  emerging  from  the  chimney  shafts  of 
improperly  worked  settings.  An  analysis  of  the  gas  drawn  from  the  waste  flues  of. 
a  retort  setting  should  approximate  very  closely  to — 

Carbon  dioxide .       .     19-0  per  cent- 
Oxygen                                         .0-4 

Nitrogen  80-6         „ 

Bi 


50  MODERN   GASWORKS   PRACTICE 

If  oxygen  is  absent,  then  CO  will  be  present,  and  the  secondary  air  should  be 
increased  until  the  required  conditions  are  obtained.  At  the  same  time,  the  above 
percentage  of  oxygen  is  quite  within  the  limits  of  practical  adjustment,  and  any 
excess  should  be  curtailed  by  a  reduction  of  the  secondary  air  supply. 

THE  EFFECT  OF  REGENERATION 

It  has  been  pointed  out  that  the  ultimate  combustion  temperature  is  governed 
in  part  by  the  temperature  of  the  mixture  before  ignition  takes  place.  This  being 
the  case,  the  quantity  of  heat  in  the  gases  before  combustion  can  be  added  to  the 
heat  of  combustion  ;  thus  the  total  quantity  of  heat  available  for  raising  the  tempera- 
ture of  the  waste  products  is  increased  in  proportion  to  the  intensity  of  the  pre- 
liminary heating.  Before  the  introduction  of  the  regenerator,  one  of  the  chief 
causes  of  loss  arose  from  the  escape  of  the  waste  products  from  the  retort  settings 
at  unnecessarily  high  temperatures,  this  occurring  in  both  "  direct-fired  "  and 
generator  settings.  In  the  latter  type  the  secondary  air  is  certainly  heated  up,  but 
merely  at  the  expense  of  the  producer  ;  and  the  system  owes  its  greater  efficiency 
mainly  to  the  reduction  of  losses  by  radiation,  to  its  flexibility,  and  to  increased  facili- 
ties for  the  regulation  of  the  air  supply.  In  such  cases  the  normal  temperature  at  which 
the  gases  are  allowed  to  leave  the  setting  is  in  the  neighbourhood  of  1,800°  Fahr.  ; 
but  by  the  transference  of  sensible  heat  from  these  gases  to  the  inflowing  secondary 
air  the  temperature  of  the  gases  has,  in  the  modern  regenerator,  been  reduced  by 
600°  to  8CO°  Fahr.  before  their  escape  is  permitted,  this  accounting  for  a  saving  in 
fuel  of  from  6  to  1  1  per  cent,  compared  with  the  generator  setting.  In  the  ordinary 
way  the  secondary  air  approaches  a  temperature  of  1,800°  Fahr.  before  combustion. 

THE   EFFECT   OF   STEAM 

It  is  unnecessary  to  enter  here  into  an  explanation  of  the  now  generally  accepted 
theory  of  reactions  taking  place  in  the  fuel-bed  during  the  formation  of  producer 
gas.  Stated  in  brief,  it  is  supposed  that  the  main  constituents  (other  than  nitrogen) 
of  true  producer  gas  are  formed  in  accordance  with  the  following  equations  :  — 

(a)  C  +  02  =  C02 
(6)  2C  -f  02=2CO 
(c)  C02  +  C  =  2CO 


The  oxygen  entering  the  base  of  the  bed  combines  with  carbon  according  to  (a) 
and  (6),  with  reaction  (a)  predominating  and  the  formation  of  C02  in  considerable 
excess.  The  C02  in  travelling  through  the  remainder  of  the  fuel  then  undergoes 
reduction  in  part  to  carbon  monoxide  as  in  (c).  By  far  the  most  important  dis- 
tinction between  the  reactions,  however,  lies  in  the  fact  that  whilst  (a)  and  (6)  are 
exothermic  and  disperse  heat,  (c)  is  endothermic  and  absorbs  heat.  In  view  of 
this  fact,  the  necessity  for  avoiding  waste  of  CO  (which  for  its  production  has  deprived 
the  producer  of  heat)  in  the  waste  gases  becomes  all  the  more  apparent. 

Some  precaution  is  necessary  in  the  procedure  of  steaming  the  fuel.  It  is  now 
the  common  practice  to  provide  water-sealed  ashpans  for  the  furnace,  so  that  ashes 


THE  HORIZONTAL  RETORT  BENCH        51 

falling  through  the  firebars  are  quenched,  with  the  formation  of  steam.  At  the  same 
time  a  longer  life  is  ensured  for  the  firebars  by  the  provision  of  a  continuous  trickle 
of  water  —  this  giving  rise  to  further  quantities  of  steam.  The  primary  duty  of  the 
steam  is  that  of  keeping  the  base  of  the  fuel-bed  cool  in  comparison  with  the 
remainder,  so  that  excessive  fluxing  of  the  ash  is  prevented,  and  the  formation 
of  clinker  curtailed.  Steam  in  passing  up  through  the  fuel  is  broken  up  into  its 
elements,  the  oxygen  combining  with  the  carbon  in  the  following  manner  — 

C+H20  =  CO+H2 

This  reaction,  being  endothermic,  deprives  the  producer  of  heat  ;  but  the  heat 
so  lost  has  been  instrumental  in  generating  a  further  quantity  of  combustible  gases 
(CO  and  H2)  which  yield  up  an  amount  not  far  short  of  the  loss,  when  burnt  in  the 
combustion  chamber  and  cooled  down  in  the  regenerator.  What  has  in  reality 
happened  is  that  heat  has  been  appropriated  from  the  producer  at  a  point  where 
excessive  temperatures  are  to  be  avoided  and  has  been  transferred,  with  a  certain 
amount  of  loss,  to  the  portion  of  the  setting  where  maximum  quantities  of  heat  are 
desired.  In  this  way  steaming,  in  spite  of  the  thermal  losses  it  occasions,  has  a  two- 
fold value.  Owing,  however,  to  the  endothermic  nature  of  this  reaction  (which 
occurs  at  high  temperatures),  the  quantity  of  steam  must  be  curtailed,  otherwise  the 
fuel-bed  will  be  inordinately  cooled,  which  may  result  in  the  oxidation  of  carbon 
to  CO  2  in  the  following  manner  — 


C+2H20=C0 

This  reaction,  being  also  endothermic,  is  depriving  the  producer  of  heat  for  the 
formation  of  an  inert  gas,  C02.  Moreover,  the  presence  of  excessive  quantities  of 
steam  is  likely  to  increase  the  tendency  of  some  of  the  CO  to  undergo  oxidation  — 

C0+H20  =C02  +  H2 

In  brief,  to  take  an  exaggerated  analogy,  all  attempts  at  working  the  producer 
on  conditions  approaching  those  of  the  water-gas  generator  (necessarily  an  inter- 
mittent operation,  owing  to  the  large  thermal  losses  during  gas-making)  are  to  be 
condemned. 

[The  practical  working  of  producers  and  economy  of  fuel  are  further  discussed 
in  Chapter  IV.] 

HORIZONTAL   BENCHES:    GENERAL   CONSIDERATIONS 

Direct-fired  furnaces,  in  spite  of  their  inefficiency,  are  still  to  be  found  (par- 
ticularly as  stand-byes)  in  a  few  of  the  country  works  of  moderate  size.  Their  chief 
recommendation  lies  in  the  fact  that  in  case  of  emergency  spare  units  can  be  put 
under  working  conditions  in  far  shorter  time  than  is  the  case  with  gaseous  settings, 
thus  avoiding  the  necessity  of  keeping  the  latter  under  slow  fires.  •  The  original  type, 
however,  with  air  supplies  entirely  uncontrolled,  is  now  giving  way  to  a  more  efficient 
design  operated  on  semi-gaseous  lines.  This  principle  is  shown  in  Fig.  17,  from 


52 


MODERN   GASWORKS   PRACTICE 


which  it  will  be  seen  that  the  air  entering  under  the  grate  is  controlled  by  dampers, 
so  that  a  portion  of  the  coke  is  burnt  to  CO  instead  of  wholly  to  C02.  A  further 
supply  of  air  (also  under  control)  is  then  admitted  above  the  fuel,  so  that  complete 
combustion  takes  place.  In  this  way  the  supply  can  be  regulated  within  finer  limits 
than  is  the  case  when  the  whole  is  admitted  under  the  grate,  and  the  excess  of  air 
in  the  flue  gases  can  be  reduced  by  more  than  one-half. 

Works  making  up  to  100  or  120  million  cubic  feet  per  annum  usually  employ 
the  10-foot  stop-ended  retort,  and  where  shovel  charging  is  in  vogue  this  system  is 


FIG.  17. — SEMI-GASEOXJS  PRODUCER. 


FIG.  19. — TYPICAL  DIRECT-FIRED 
FURNACE. 


FIG.  18. — TEN-FOOT  "THROUGH"  RETORT  BENCH. 


undoubtedly  the  most  suitable.  A  recent  introduction,  however,  is  the  10-foot 
through  bench  seen  in  Fig.  18 ;  whilst  typical  stop- ended  settings  are  shown  in 
Figs.  19  and  20.  The  single  through  bench  has  the  advantage  that  discharging 
machinery  may  be  used  ;  and,  the  back-end  of  the  retort  being  close  up  to  the  retort- 
house  wall,,  the  coke  can  be  pushed  direct  into  the  yard.  A  modern  favourite  for 
medium-sized  works  making  from  120  to  2CO  millions  per  annum  is  the  14-foot 
through  retort,  which  may  be  suitably  operated  by  some  of  the  present-day  types  of 
discharging-chargers. 

The  following  average  dimensions  are  given  for  the  various  types  of  benches 
with  their  houses  : — 


THE  HORIZONTAL  RETORT  BENCH 


53 


ft,  in. 

1.  Single  bench :     1  6  at  back  of  bench. 

12  6  for  bench  (11  feet  6  inches  if  retorts  are  9  feet  long). 

18  0  in  front. 


32     0     over-all  width  inside  house. 


The  height  of  the  bench  would  be  about  11  feet  from  ground-level,  and  the  height  of  the  house 
to  the  eaves  20  to  21  feet. 

2.  Through  bench  (scoop  charging  and  no  machinery) — 
Bench,  20  feet. 
Each  side  of  bench,  18  feet. 
Total  width  of  house,  56  feet  inside. 

Height  of  bench  from  top  of  foundation  to  top  of  brickwork,  nearly  20  feet  for  3  tiers. 
Height  of  house  to  eaves  (stage  type),  about  35  feet. 

3.  Through     bench      (charging 
and     discharging 
machinery) — 
Zf-%^  Bench,  20  feet. 

Charging  side,  23  feet. 
Discharging  side,  17  feet. 
Total  width    of    house,    60 

feet. 

Height  of  bench  from  top 
of  .foundation  to  top 
of  brickwork,  24  feet 
6  inches  to  26  feet  for 
5  tiers. 

Height  of  house  to  eaves 
(stage  type),  41  feet, 
with  continuous  hop- 
pers. 

Height  of  house  to  eaves 
(stage  type),  36  feet, 
with  hoppers  between 
roof  trusses. 

The     height      of     the 
bench    naturally     depends 


"6'x5"R.S.J.[ 


f 


FIG.  20. — REGENERATIVE  STOP-END  SETTING. 


54 


MODERN   GASWORKS   PRACTICE 


upon  the  number  of  tiers  in  which  the  reto.rts  are  set,  and  an  approximate  rule 
gives  an  allowance  of  29  inches  of  height  for  each  tier.  This  gives  the  distance 
from  charging  floor  to  the  soffit  of  the  main  arch.  Thus  for  a  setting  of  10's  in  two 
rows  of  5  the  height  to  the  underside  of  the  arch  would  be  approximately  12  feet. 
For  a  setting  of  8's  in  three  rows  the  height  would  be  8  feet  to  8  feet  9  inches.  So 
far  as  the  width  of  the  main  arch  is  concerned  the  dimensions  (from  inside  to  inside 
of  pier  walls)  are  as  follows  : — 

Fpr  two  rows  :    7  feet  9  inches  to  8  feet  9  inches,  depending  on  the  size  of  retorts  employed. 
For  three  rows  :  8  feet  6  inches  to  9  feet  „  „  „  ,, 

Where  shovel  or  scoop  charging  is  employed,  it  is  inadvisable  to  have  more  than 
three  superimposed  tiers  of  retorts,  otherwise  a  movable  stage  has  to  be  used. 

CONSIDERATIONS   IN  DESIGN   OF   THE   SETTING 

The  question  of  the  capacity  of  various  units  has  already  been  discussed  in 

Chapter  I  (page  12). 
In  the  smaller  works 
the  unit  is  of  more 
importance,  owing  to 
the  necessity  of  pro- 
viding for  comparatively 
small  fluctuations  in  out- 
put. For  this  reason  it 
is  common  to  find  arches 
of  varying  capacity,  as  is 
seen  in  the  retort  bench 
shown  in  Figs.  21  and  22. 
In  the  medium  and  large 
sized  works  the  smaller 
fluctuations  can  best  be 
coped  with  by  the  use  of 
a  water-gas  plant. 

While  the  design  of 
the  direct-fired  setting  is 
comparatively  simple, 
the  various  portions  of 
the  gaseous  setting  re- 
quire particular  care  and 
experience  if  the  many 
demands  made  upon  it 
are  to  be  satisfactorily 
met.  In  connection  with 
the  direct  setting  the 
FIG.  21.— RETORT  BENCH  WITH  VARYING  UNITS.  following  points  in  con- 


THE  HORIZONTAL  RETORT  BENCH 


55 


struction  and  •  working  may  be  given  separate  notice,  although  many  of  those 
hereafter  classified  under  gaseous  settings  also  apply  : — 

(a)  Where  the  longer  retorts  (9  feet  and  10  feet)  are  employed,  attention  must  be 
given  to  the  method  of  heating  the  back-ends,  otherwise  the  last  foot  or  so  will  be 
dull  in  comparison  with  the  remainder.  This  is  best  coped  with  by  building  a 
special  double  chamber  at  the  back-end,  thus  ensuring  the  thorough  circulation  of  the 
gases  around  the  retort  at  this  point. 

(6)  The  air  supply  should  be  regulated,  and  split  up  into  a  primary  and  secondary 
supply  (semi-gaseous)  where  possible. 

(c)  Steaming  the  fuel-bed  should  be  reduced  to  a  minimum.  In  this  type  of 
furnace  the  waste  products  escape  at  high  temperatures,  and  the  heat  required  to 


FIG.  22. — REGENERATOR  RETORT  BENCH  WITH  VARYING  UNITS. 

raise  the  steam  to  the  temperature  of  the  setting  is  appropriated  from  the  heat 
produced  by  the  combustion  of  the  coke — hence  the  steam  occasions  a  direct  loss. 
This  also  applies  to  the  generator  system,  but  does  not  occur  to  nearly  the  same 
extent  in  regenerator  settings,  where  the  waste  products  are  cooled  considerably 
before  escaping. 

Water-cooled  firebars  should  be  avoided. 

(d)  All  flues  must  be  accessible  for  cleaning  while  the  setting  is  at  work. 

(e)  The  possibility  of  short-circuiting  between  the  flues — a  common  fault  with 
these  settings — must  be  provided  against. 

(/)  The  loss  of  heat  through  the  walls  of  the  furnace  by  radiation  is  proportional 
to  the  size  of  the  furnace  ;  thus  the  furnace  having  the  smallest  heat-radiating  sur- 
face will  be  the  most  economical. 

(g)  The  further  back  the  actual  fire  stretches,  the  better  will  be  the  heating  of 


56 

the  back  of  the  retorts  ;  on  the  other  hand,  very  long  grates  are  difficult  of  access  for 
•cleaning,  etc. 

(h)  If  a  deep  fuel-bed  is  employed  CO  will  be  formed,  and  escaping  unburnt  will 
;  account  for  considerable  loss.  In  the  smaller  grates  12  inches  of  fuel  depth  is  ample. 
It  should  not  in  any  case  exceed  18  inches,  unless,  of  course,  a  supply  of  secondary 
air  above  the  fuel  is  arranged  for.  This  point  is  often  difficult  to  impress  upon  the 
•country  stoker,  as  charging  the  furnace  little  and  often  entails  considerably  more 
trouble. 

(i)  The  front  of  the  fire  (above  the  firebars)  must  either  be  sealed  with  a  plate 
or  breezed  up  so  that  all  air  enters  beneath  the  firebars. 

(j)  The  furnace  linings  should  be  isolated  from  the  remainder  of  the  brickwork, 
and  not  bonded  in  in  any  way.  The  wear  and  tear  with  this  type  of  furnace  is 
extremely  heavy,  and  the  furnace  requires  frequent  re-lining. 

(k)  The  stop  end  of  the  retort  frequently  breaks  away  after  the  bench  has  been 
working  for  some  time,  and  as  bricks  will  then  have  to  be  inserted  it  is  as  well  to 
brick  up  the  end  (4|  inches)  before  the  retort  is  put  to  work  in  the  first  place. 

(I)  When  starting  up  settings  care  must  be  taken  to  avoid  explosions.  The 
chances  of  explosions  occurring  in  direct  settings  are  remote,  but  the  experience  is 
by  no  means  unknown.  (For  further  information,  see  page  87  et  seq.) 


GENERATOR  AND   REGENERATOR  SETTINGS 

The  essential  difference  between  generator  and  regenerator  settings  is  in  the 
means  employed  for  circulating  the  waste  gases  and,  in  the  latter  type,  for  extracting 
the  maximum  quantity  of  sensible  heat  from  them  before  their  escape.  In  the 
generator  type  the  main  waste-gas  flue  travels  along  the  top  of  the  main  arches,  with 
the  chimneys  carried  up  at  intervals,  whilst  in  the  regenerator  system  the  waste 


FIG.  23. — DOUBLE  FURNACE. 


FIG.  24. — SINGLE  FURNACE. 


flue  generally  runs  longitudinally  through  the  entire  bench,  practically  at  foundation- 
level.  Another  important  distinction  is  that  with  generator  settings  a  double  furnace 
(Fig.  23)  is  usually  employed,  whilst  the  single  furnace  (Fig.  24)  is  now  exclusively 
used  with  the  regenerator  bench.  The  latter  embraces  the  advantages  of  reduced 


THE  HORIZONTAL  RETORT  BENCH 


57 


labour  in  charging  and  clinkering,  more  effectual  control  of  heats,  less  wear  and  tear, 
and  considerably  improved  working  conditions  for  the  men.  Generator  settings  are 
seldom  used  in  conjunction  with  "  through  "  retorts. 

So  far  as  the  design  of  the  modern  regenerator  furnace  is  concerned,  a  typical 


.  B 

SECTION  THKOUGH  FURNACE  AND  COMBUSTION  CHAMBER 

FIG.  25.— A  TYPICAL  HORIZONTAL  REGENERATOR  RETORT  BENCH. 


working  drawing  is  shown  in  Figs.  25.  25A  and  25s,  whilst  a  sectional  diagram  of 
the  same  type  of  setting  is  given  in  Fig.  26.  The  various  portions  of  the  setting 
and  the  considerations  to  be  kept  in  view  in  order  to  ensure  long  life  and  effective 
working  are  dealt  with  under  their  respective  headings. 


58 


MODERN   GASWORKS. PRACTICE 


(a)  MAIN  ARCHES 

The  stability  of  the  bench  must  be  ensured,  and  the  tendency  of  the  pier  walls 
to  lean  slightly  from  the  vertical  (due  to  the  thrust  of  the  main  arches)  must  be 
checked  by  the  erection  of  substantial  end  walls  and  suitable  bracing.  When  the 


L-4L-B    LL41-.L 


SECTION  THROUGH  WASTE  GAS  FLUES 
FIG.  25A. 

bench  contains  more  than  (say)  four  beds,  these  buttress  walls  should  never  be  built 
less  than  double  the  thickness  of  the  ordinary  pier  walls,  whilst  it  is  only  necessary 
to  construct  the  inner  9  inches  of  firebricks.  For  reasons  mentioned  later  (see 
page  154)  an  ordinary  hard  stock  brick  of  good  quality  and  shape  is  perfectly  suit- 
able and  desirable  for  the  remainder  of  the  work. 


.  THE  HORIZONTAL  RETORT  BENCH       59 

* 

As  a  general  rule  an  18-inch  wall  between  the  arches  will  suffice  for  all  typea 
of  settings,  and  the  two- and- a- half  brick  wall  occasionally  seen  is  wholly  unneces- 


~r    r 


i-    i 


i  I 

LI. 


KMl- 


mfe£ 

Wi 

F  i-ii 
HKlii 


"•""  * 

—  1_ 

T 

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_it: 

^r     r^-T-.L^JJ 

| 

IJ.^  —  I  [__ 

-  

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TTIT  i  ri  *  r 
—  JLf:...J_Ti.l;  —  T-TJ;  ._..   , 

T 

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....  :  ill.,...  .1          i 

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~"T 

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t> 

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sary.     Such  walls  are,  of  course,  entirely  constructed  from  firebricks,  these  being 
carried  up  round  the  main  arches  to  a  depth  of  9  inches.     Beyond  this,  any  further 


MODERN   GASWORKS   PRACTICE 


FIG.  26. — SECTIONAL  DIAGRAM  or  HORIZONTAL  REGENERATOR  SETTING. 

brickwork  required  for  filling  up  the  spandrils,  etc.,  may  be  of  ordinary  stock-work 
or,  if  preferred,  old  firebricks  well  cleaned.     A  reveal  (as  shown  in  Fig.  27)  should 


THE  HORIZONTAL  RETORT  BENCH 


61 


Spandril 


be  left  in  the  pier  walls  and  arches  so  that  a  tight  joint  is  obtained  when  the  front 
wall  goes  up. 

The  semicircular  main  arch  is  the  ideal,  as  it  accounts  for  practically  no  hori- 
zontal thrust  on  the  side  walls.  With  settings  of  two  vertical  rows  the  semicircle 
should  always  be  employed ;  but 
the  greater  width  necessary  with 
three  or  four  vertical  rows  makes 
the  use  of  such  an  arch  somewhat 
inconvenient.  In  such  cases  ellipti- 
cal or  segmental  arches  are  often 
erected,  as  in  this  way  excessive 
headroom  above  the  top  tier  of 
retorts  is  avoided.  Care  must  be 
taken,  however,  to  see  that  decidedly 
flat  arches,  liable  to  failure,  are 
abstained  from.  A  generally  recog- 
nized rule  is  to  the  effect  that  no  arch  should  have  a  radius  of  more  than  7  feet  6 
inches.  Many  designers  will  hear  of  nothing  else  but  a  semicircular  arch,  whatever 
the  type  of  setting.  It  is  maintained  that  the  excessive  headroom  does  not 
matter  in  the  least,  and,  if  necessary,  can  be  tiled  in  and  isolated.  The  increased 
cost  entailed  is  comparatively  insignificant. 

All  types  of  arches  are  generally  built  from  concentric  rings  of  brickwork, 
although  a  growing  (but  more  expensive)  practice  is  to  employ  special  radius  blocks. 
When  the  brick  arch  is  used,  however,  there  should  never  be  less  than  three  rings,  as 
it  is  impossible  to  prevent  some  sagging  of  at  least  the  lowest  ring  after  the  arch 


36" 

Buttress 
Wall 


18  Pier  Wall 

FIG.  27. — MAIN  ARCHES  FOR  RETORT  SETTINGS. 
THE  BLACKED  PORTION  INDICATES  FIRE-BRICK. 


FIG.  28. — BARREL- SHAPED 
SETTING  ARCH. 


FIG.  29. — SUPPORT  FOR  SOFFIT  OF  MAIN  ARCH. 


has  been  in  operation  for  some  time.  To  overcome  this  drawback  the  barrel-arch 
with  a  camber  in  both  directions  (Fig.  28)  has  been  introduced  with  success,  but 
owing  to  increased  expense  must  be  looked  upon  as  a  luxury.  A  simple  and  effec- 
tive means  of  preventing  the  dropping  of  the  inmost  ring  is  to  stay  up  the  soffit  of 


MODERN   GASWORKS   PRACTICE 


FIQ.  30. — SEGMENTAL  ARCH  WITH 
AIR  CHANNELS. 


the  arch  by  means  of  tiles  supported  from  the  cross-walls  of  the  setting  (Fig.  29). 
It  should,  however,  be  seen  that  expansion  of  the  work  below  is  allowed  for,  by  leav- 
ing a  space  between  the  top  of  the  tiles  and  the  soffit  of  the  arch.  Two  inches  will 
usually  answer  the  purpose.  The  difficulty,  however,  lies  in  gauging  the  amount 
of  expansion,  so  that  when  the  setting  is  heated  up  the  soffit  just  rests  on  the  tiles. 
Obviously,  if  there  is  a  space  between  the  two  the  tiles  are  useless,  whilst  if  over- 
expansion  takes  place  they  are  actually  harmful. 

In  America,  some  attempt  has  been  made  to  reduce  the  losses  of  heat  from 
radiation  by  leaving  cavities  around  the  main  arches,  or  by  employing  special  channel 
blocks  (Fig.  30).  The  practice,  however,  cannot  be  recommended,  as  the  stability 

of  the  work  is  seriously  affected,  and  radiation  losses 
will  not  be  excessive  if  the  brickwork  is  carried  up 
at  least  18  inches  above  the  top  of  the  arch  rings. 
As  a  further  precaution  it  is  as  well  to  plaster  the 
top  of  the  bench  with  a  thin  layer  (2  inches)  of 
some  non-conducting  material.  This  can  be  effec- 
tively made  from  waste  rope  dust  and  rough  asbestos 
composition  composed  of  ten  parts  of  the  former,  to 
one  part  of  asbestos.  The  rope  dust  costs  about  15s. 
per  ton,  the  asbestos  £5  10s.  and  the  work,  including 
the  labour,  can  be  carried  out  for  3s.  Gd.  per  square 
yard. 

An  objectionable  practice,  which  is  happily  dying  out,  is  that  of  filling  up  the 
spandrils  of  the  main  arches  with  sand  and  putting  a  paving  of  bricks  on  the  top 
of  this.  Far  from  preventing  radiation,  the  sand,  owing  to  its  close-lying  nature,  is 
always  accompanied  by  excessive  losses  in  this  respect ;  and  in  time,  when  the  work 
gets  old,  the  sand  is  likely  t6  drain  through  crevices,  leaving  hollow  spaces  in  the 
spandrils  and  giving  trouble  in  the  settings  owing  to  its  low  fusing  point. 

(6)  THE  PRODUCER 

Through  retort  benches  should  in  all  cases  be  fired  with  the  single  rather  than 
the  double  furnace,  as  in  this  way  a  saving  of  from  10  to  15  per  cent,  in  fuel  consump- 
tion can  be  looked  for.  The  primary  consideration  is  that  of  ensuring  ample  depth 
of  fuel-bed,  so  that  the  reduction  of  carbon  dioxide  to  carbon  monoxide  may  effec- 
tively take  place.  In  the  larger  regenerative  settings  of  8's  and  10's  it  is  preferable 
to  allow  for  not  less  than  7  feet  from  the  mean  level  of  the  firebars  to  the  springing 
of  the  producer  arch,  although  in  the  smaller  units  this  will  often  be  no  more  than 
5  feet.  As  regards  shape,  the  internal  producer  is  always  rectangular.  Al- 
though on  certain  scientific  grounds  it  should  be  square  (due  to  the  fact  that 
of  rectangular  figures  the  square  has  the  smallest  perimeter  for  a  given  area,  thus 
exposing  the  minimum  amount  of  wall  surface),  it  is  commonly  constructed  with 
the  front  width  about  half  the  distance  which  it  extends  backwards  at  the  base. 
The  reason  for  this  is  that  construction  is  facilitated,  a  better  distribution  of  pro- 
ducer gas  results,  ample  room  is  left  for  the  regenerator  device,  and  the  front  wall 


THE  HORIZONTAL  RETORT  BENCH 


area  is  comparatively  small.  This  last  is  an  important  point,  in  that  heat  radiat- 
ing through  the  wall  is  lost,  whereas  in  the  longer  side  walls  it  is  partly  picked  up 
by  the  inflowing  secondary  air  and  recovered.  Further  considerations  which  must 
receive  attention  are  the  following : — 

(1)  The  producer  lining  should  be  entirely  separate  from  the  main  body  of 
the  brickwork.     The  wear  and  tear  on  this  portion  of  the  setting  is  heavier  than 
that  on  any  other  portion,  and  although  a  well-built  and  substantial  lining  will  re- 
main in  workable  condition  for  about  600  to  800  days,  minor  repairs  are  often  neces- 
sary every  year.     Shutting  down  and  restarting,  however,  is  to  be  avoided  as  far  as 
possible,  owing  to  the  undesirable  effect  on  the  working  life.     The  false  cheeks  to  the 
producer  may  be  built  up  of  a  4^-inch  or  9-inch  wall.     The  latter  is  preferable,  and 
the  bricks  should  be  laid  all  "  headers,"  so  that  considerable  wear  can  take  place 
without  the  bond  of  the  work  being  broken. 

(2)  The  lowest  point  of  the  charging  door  frame  of  the  producer  should  be  no 
higher  than  the  soffit  of  the  furnace  arch,  and  the  frame  should  be  sloped  at  such  an 
angle  as  to  enable  the  coke  at  the  back  of  the  furnace  to  be  seen,  and  to  be  reached 
with  a  rake. 

(3)  The  lower  portion  of  the  producer  should  be  slightly  narrower  than  the 
upper  portion.     That  is,  at  a  point  about  level  with  the  top  of  the  furnace  frame  the 
brickwork  should  be  set  back  2£  inches  at  the  sides.     This  will  prevent  the  short- 
circuiting  of  primary  air  up  the  sides  of  the  fuel-bed. 

(4)  The  primary  air  should  preferably  be  admitted  through  slides  in  the  fur- 
nace door,  and  not  by  means  of  channels  passing  through  the  brickwork  at  the  side 
of  the  furnace.     Such  channels  usually  give  trouble  by  chok- 
ing up,  whilst  short-circuiting  of  the  primary  air  up  the  front 

of  the  fuel-bed  may  be  avoided  by  "  breezing  up." 

The  general  practice  is  to  build  up  the  producer  with 
parallel  side  walls,  a  semicircular  furnace  arch  being  thrown 
over  these  (Fig.  25B).  In  some  cases  additional  strength  is 
given  to  the  producer  by  arching  out  the  side  walls  as  in  Fig. 
31,  but  the  advantages  accruing  from  this  arrangement  can 
scarcely  be  said  to  compensate  for  the  increased  cost.  The 
widening  out  of  the  furnace  in  this  way  also  prevents  the 
short-circuiting  of  air  through  the  fuel-bed.  One  or  two 
sets-off  of  bricks  should  be  arranged  for  at  the  back  of  the 
producer,  and  the  remaining  work  taken  up  at  a  wide  angle 
with  the  horizontal.  Whatever  the  shape  of  the  producer, 
the  front  wall  should  be  of  18-inch  thickness,  and  there 
should  not  be  less  than  9  inches  solid  work  between  the  side 
walls  of  the  furnace  and  the  regenerator  flues. 


FIG.    31.    -  -    ARCHED 
PRODUCER. 


(c)  GRATE  AREA 

The  recognized  modern  rule  is  that  of  allowing  y1^  square  foot  of  grate  area 
for  each  lineal  foot  of  retort  in  the  setting,  and  for  effective  working  this  should  be 


64  MODERN   GASWORKS   PRACTICE 

looked  upon  as  the  irreducible  minimum.  For  a  through  setting  of  ten  retorts  the 
rule  gives  a  grate  area  of  20  square  feet.  There  is  little  doubt  that  the  producer 
now  used  in  conjunction  with  the  continuous  vertical  retort  owes  its  economy  in 
part  to  the  increased  grate  area  allotted.  In  the  Woodall-Duckham  system  this 
amounts  to  as  much  as  28  square  feet  for  each  producer,  or  rather  more  than 
£  square  foot  per  lineal  foot  of  retort  in  the  bench.  Mr.  Thos.  Glover  has  stated  that 
with  certain  coals  a  grate  area  of  f  square  foot  per  10  feet  6  inch  run  of  retort  is 
sufficient,  but  with  other  coals,  containing  different  proportions  of  lime  and  iron  in 
the  ash,  the  clinker  is  difficult  to  remove.  Another  rule  is  that  of  allowing  1  square 
foot  of  area  for  each  8  Ib.  of  coke  consumed  by  the  furnace  per  hour.  This  basis, 
however,  is  not  altogether  satisfactory,  as  the  fuel  consumption  is  arrived  at  by 
guesswork,  and  necessarily  varies  with  the  type  of  coke  in  use. 

(d)  FLUE  AND  CHIMNEY  AREA 

The  retort-house  chimney  in  large  houses  varies  from  50  to  70  feet  in  height. 
The  chief  considerations  to  be  kept  in  mind  are  that  of  taking  it  well  above  any 
adjoining  buildings,  and  that  down-draughts  and  varying  winds  are  avoided.  With 
direct-fired  and  generator  furnaces  it  is  usual  to  support  the  chimney  from  the  top 
of  the  bench  and  to  run  the  main  waste-gas  flue  directly  into  it.  With  the  regen- 
erator setting,  however,  the  chimney  is  usually  sprung  from  foundation- level,  and 
should  preferably  be  .entirely  distinct  from  the  bench.  So  far  as  its  constructional 
features  are  concerned,  the  cross-sectional  area  is  the  most  important,  and  must  in 
all  cases  be  adequate.  The  usual  rule,  which  may  be  applied  with  perfect  reliance, 
is  to  allow  1J  square  inches  of  area  per  lineal  foot  of  retort  in  all  settings  dependent 
upon  the  flue  and  chimney.  Thus,  suppose  a  bench  consisting  of  eight  settings -of 
"  tens  "  is  to  work  on  to  a  common  flue  and  chimney — 

The  length  of  retort  in  each  setting  is  200  feet. 

The  length  of  retort  in  eight  settings  is  1,600  feet. 

The  chimney  area  required  is  1,600  X  1^  square  inches,  i.e.  2,400  square  inches, 
or  16|  square  feet. 

With  large  units  of  through  settings  75  per  cent,  of  this  is  sufficient. 

Another  rule  (due  to  Herring)  is  that  of  allowing  40  square  inches  per  ton  of 
coal  carbonized  per  diem  by  the  whole  bench  of  retorts  dependent  on  the  chimney. 
The  following  formula  (Brooke)  is  also  sometimes  used  : — 

5W 

A  =  —7=- 

VH 

Where  A   =  area  of  chimney  in  square  feet. 
H  =  height  of  chimney  in  feet. 
W  =  weight  of  fuel  burnt  per  minute,  in  Ibs. 

In  any  case,  when  a  shaft  is  to  be  erected  it  should  be  based  upon  the  first  of 
the  rules  here  given,  and  the  last  named  may  be  used  as  a  means  of  checking.  It 
is  inadvisable  to  connect  a  chimney  to  a  greater  number  of  beds  than  ten,  as  above 
this  (at  any  rate  for  settings  of  10's  or  12's)  its  dimensions  become  somewhat 


THE  HORIZONTAL  RETORT  BENCH 


65 


18 


2  3 


3' 9" 


.unwieldy.  Circular  shafts,  except  for  some  vertical  installations, 
may  now  be  said  to  be  things  of  the  past,  and  the  rectangular 
chimney  with  external  batter  is  most  commonly  seen.  A  typi- 
cal design  of  this  style  of  shaft  is  seen  in  Fig.  32.  It  will  be 
noticed  that  a  square  base  10  feet  in  height  is  provided.  Some 
ornamentation  (such  as  oversailing  courses,  plinths,  or  panel- 
ling in  different  coloured  bricks)  is  usually  added.  The  batter 
commences  immediately  above  the  square  base,  and  is  usually 
run  in  the  ratio  of  1  to  36  or  1  to  40.  A  point  to  remember  is 
that  the  calculated  chimney  area  refers  to  the  area  at  the  base 
of  the  shaft,  and  the  design  should  be  such  that,  in  spite  of  the 
reduction  of  thickness  of  the  brickwork,  the  cross- sectional  area 
at  the  summit  is  the  same.  In  Fig.  32  a  batter  of  1  in  40 
gives  an  over- all  reduction  in  total  width  of  3  feet,  and  at  both 
top  and  bottom  the  internal  dimensions  are  similar,  namely 
3  feet  9  inches  square. 

So    far    as  the    thickness    of  chimney  walls  is  concerned, 
the  following  typical  instances  for  various  heights  are  given  : — 

(a)  68  feet  high. 

Brickwork  :   1  foot  10£  inches  for  12  feet. 

1  foot    6    inches  for  16  feet. 

1  foot     1J  inches  for  20  feet. 

9     inches  for  20  feet. 

1  foot  10£  inches  for  12  feet,  reducing  to  9  inches 
at  top.     Outside  batter  1  in  36. 

1  foot  10 \  inches  for  11  feet. 

1  foot     6     inches  for  14  feet. 

1  foot     1J  inches  for  16  feet. 

9     inches  for  17  feet. 

A  small  proportion  of  chimneys  is  now  to  be  found  in  which  the  brickwork  is 
reduced  to  4|-inch  for  some  distance  in  the  upper  length.  It  must  be  strongly 
emphasized,  however,  that  such  design  is  to  be  rigidly  avoided,  the  more  so  in  retort- 
house  shafts,  where  wind  and  heat  have  both  to  be  withstood.  Chimneys  of  this 
description  are  occasionally  to  be  met  with  in  which  no  external  batter  has  been 
provided,  the  walls  running  up  vertically  from  base  to  top.  For  instance,  a  group 
of  retort- house  shafts  is  known  which  are  constructed  as  follows :  The  shafts  are 
70  feet  in  height,  the  first  30  feet  being  13|-inch  brickwork,  the  next  20  feet  9-inch 
brickwork,  and  the  final  20  feet  4|-inch  work.  In  the  4|-inch  portions  the  corners 
are  constructed  of  6-inch  work  for  increased  stability.  The  effect  of  such  design 
on  chimney  area  is  well  illustrated  by  reference  to  Fig.  33.  The  effective  area  at 
the  base  is  14  square  feet ;  whereas  at  the  9-inch  work  it  has  been  increased  to 
27  £  square  feet,  or  nearly  double. 

Retort-house  chimneys  are  usually  braced  for  their  entire  height,  the  most 
general  method  being  to  run  angle-iron  up  each  corner,  the  irons  being  held  in  posi- 

F 


(b)  65  feet  high. 

Brickwork 

(c)  58  feet  high. 

Brickwork  ; 


FIG.  32. — CHIMNEY 
WITH  EXTERNAL 
BATTER. 


66 


MODERN   GASWORKS   PRACTICE 


FIG.  33. — SHOWING  OBJEC- 
TION TO  UNTAPERED 
CHIMNEY. 


tion  by  tie-bars  at  intervals  of  about  6  feet.  The  shaft  used  in  conjunction  with 
regenerator  settings  may  be  centrally  divided  by  a  4^-inch  wall  in  the  same  manner 
as  the  main  waste-gas  flue.  It  is  always  advisable  to  leave  inspection  doors  at  the 
base  of  the  shaft,  so  that  the  condition  of  the  waste-gas  flue  can  be  readily  seen  dur- 
ing working,  and  a  vacuum  gauge  inserted ;  -whilst  pro- 
vision should  be  made  for  a  cleaning  door,  so  that  dust, 
etc.,  may  be  removed  during  stoppage.  The  same  door 
is  also  useful  for  the  insertion  of  a  coke  bucket  when  start- 
ing up,  in  order  that  a  natural  draught  may  be  stimulated. 
On  the  Continent  it  is  occasionally  the  practice  to  erect  a 
distinct  chimney  for  each  bench  of  retorts.  It  is  claimed 
that  in  this  way  each  furnace  may  be  worked  indepen- 
dently, whilst  with  the  common  chimney  one  furnace  may 
influence  another.  The  idea,  however,  is  confined  almost 
wholly  to  stop- ended  retort  settings. 

As  regards  the  bricks  for  the  construction  of  retort- 
house  chimneys,  where  stock-work  is  used  a  firebrick 
lining  should  be  provided  for  the  lower  half.  Nowadays, 
however,  it  is  far  more  common  for  the  whole  chimney 
to  be  built  of  firebricks,  in  which  case  no  lining  is  neces- 
sary. 

Natural  draught  depends  for  its  action  on  the  difference  of  density  between 
the  cold  air  surrounding  the  shaft  and  the  warm  products  of  combustion.  More- 
over, the  quantity  of  gas  drawn  up  by  a  chimney  increases  in  proportion  to  the 
square  root  of  the  height  of  the  chimney  ;  consequently  any  increase  in  height  pro- 
duces only  a  comparatively  small  change  in  the  quantity  of  gases  drawn  off.  As 
a  matter  of  fact,  a  shaft  creates  the  best  draught  when  the  temperature  of  the  issu- 
ing gases  differs  from  the  atmospheric  temperature  by  523°  Fahr.  Accord- 
ingly, when  the  difference  between  the  two  temperatures  is  greater  than  this  the 
draught  is  not  so  good,  and  a  larger  and  useless  loss  of  heat  takes  place.  On  the 
other  hand,  the  heat  carried  off  by  the  escaping  gases  must  not  all  be  considered  as 
loss,  for  a  certain  temperature  is  necessary  for  the  creation  of  a  natural  draught. 

(e)  REGENERATION 

Regenerators  and  generators  of  various  types  may  be  primarily  classified  as 
follows : — 

Ordinary  generators. 

(1)  Primary  and  secondary  air  supply  both  unheated. 

(2)  Primary  supply  unheated.     Secondary  heated,  but  at  expense  of  pro- 

ducer. 

(3)  Primary  and  secondary  supplies  both  heated  at  expense  of  producer. 
Regenerators. 

(1)  Primary   unheated.     Secondary   heated   by   sandwiching  between   pro- 
ducer and  waste  gases.     This  is  by  far  the  commonest  type. 


THE  HORIZONTAL  RETORT  BENCH 


67 


(2)  Primary   unheated.     Secondary,  heated   by   sandwiching   between   two 

streams  of  waste  gases.  In  this  way  the  producer  is  not  deprived  of 
heat. 

(3)  Primary  unheated.     Waste  gases  sandwiched  between  two  streams  of 

secondary  air. 

(4)  Primary  and  secondary  supplies  both  heated  by  waste  gases. 

(5)  Primary  or  secondary  air  initially  heated  by  the  extraction  of  sensible 

heat  from  the  hot  coke  in  the  retort.  That  is  to  say,  in  reality  the  coke 
leaving  the  retort  is  quenched  by  the  ingoing  air  supply.  This  arrange- 
ment is  only  practicable  with  vertical  retort  systems  of  the  continuous 
type. 

With  regard  to  the  merits  of  the  various  systems,  in  the  case  of  the  ordinary 
generator  no  use  is  made  of  the  heat  in  the  waste  gases,  and  the  secondary  or 
primary  air  is  raised  in  temperature  entirely  at  the  expense  of  the  producer.  Com- 
pared with  no  initial  heating  of  the  air  supply  the  system  does,  however,  effect 
some  economy  in  that  the  air  appropriates  part  of  that  heat  which  would  otherwise 
be  lost  by  radiation.  It  is  in  connexion  with  this  point  that  so  much  diversity  of 
opinion  exists  with  regard  to  regeneration  by  means  of  waste  gases.  Many  author- 
ities assert  that  to  admit  secondary  air  through -channels  adjacent  to  the  producer 
(Figs.  26  and  41)  is  uneconomical,  and  for  this  reason  provision  is  made  for  entirely 
encircling  the  air  with  waste  gases  as  in  Figs.  37  and  40.  In  support  of  this  theory 
Brooke  gives  the  following  figures  :— - 


Percentage  Efficiency 
of  Regenerator. 

Percentage  of  Total 
Heat  in  Secondary  Air 
abstracted  from 
Producer. 

Outside  producer       ... 

100 

» 

Inside  producer.     Air  flue  sandwiched  between 
waste  gases      ; 

90  95 

^   10 

Waste-gas  flue  between  air  supplies  .... 
Air  flue  between  side  of  producer  and  waste-gas 
flue   

80-90 
70  80 

10-20 
90   30 

Air  flue  by  side  of  producer    

6 

94 

Too  much  attention  must  not,  however,  be  paid  to  this  point ;  and  it  must  be 
remembered  that  heat  will  inevitably  pass  outwards  from  the  hot  producer  walls 
and  cause  loss  by  radiation.  Thus,  if  the  secondary-air  flue  is  adjacent  to  the  pro- 
ducer, it  will  undoubtedly  account  for  a  reduction  in  the  loss  from  this  source.  In 
practical  working  the  distinction  between  the  two  types  (1  and  2)  cannot  be  said 
to  have  a  noticeable  effect  on  fuel  consumption. 

When  choice  of  a  regenerator  is  to  be  made  consideration  should,  in  turn,  be 
given  to  the  following  items : — 

(1)  The  surface  contact  between  the  regenerator  flues  and  the  secondary- air 
flues  must  be  ample. 


68 


MODERN   GASWORKS   PRACTICE 


(2)  Every  precaution  must  be  taken  to  ensure  that  no  short-circuiting  takes 
place.     According  to  the  construction  of  the  regenerator  this  may  occur : — 

(a)  Between  secondary-air  flues  and  waste-gas  flues. 
(6)  Between  producer  and  secondary-air  flues, 
(c)  Between  producer  and  waste-gas  flues. 

(3)  There  must  be  ample  facilities  for  the  removal  of  dust,  etc.,  from  both  waste- 
gas  and  secondary-air  flues.     In  some  types  of  regenerator  no  cleaning  is  possible 
until  the  whole  is  demolished. 

(4)  Means  for  regulation  of  the  secondary  air  should  be  provided.     It  is  fre- 
quently found  that  the  currents  of  air  to  the  various  "  nostrils  "  vary  in  quantity 
to  a  considerable  extent.     For  this  reason  dual  or  multiple  regulation  is  arranged 
for  in  some  types  (see  Figs.  25s  and  40). 

(5)  The  baffling  arrangement  in  the  secondary-air  flues  should  not  be  too  in- 
volved, otherwise  an  excessive  draught  will  be  necessary  in  order  to  pull  the  requisite 
quantity  of  air  through.     High  velocity  of  draught  means  too  rapid  travel  of  the 
waste  gases,  which  consequently  leave  the  setting  before  effecting  the  maximum 
exchange  of  heat.     It  is  difficult  to  give  any  figure  for  the  thickness  of  regenerator 
blocks,  and  a  medium  has  to  be  struck  so  as  to  afford  both  good  conductivity  and 
stability. 

TYPES  OF  EEGENERATORS 

The  principle  of  operation  of  regenerators  is  best  understood  by  reference  to  dia- 
grams, and  several  illustrations  of  the  most  notable  types  are  here  reproduced.     One 

of  the  best-known  systems  which  came  into  use  in  the 
earliest  days  of  regeneration  was  the  Klonne.      In 
this  the  interchange  of  heat  was  brought  about  by 
the  employment  of  special  blocks  as  shown  in  Fig. 
34.      In  the  Gibbons  and  Masters'  system  slotted 
fireclay    boxes,    moulded    out    by    machinery,    are 
erected  side  by  side  in  vertical  tiers  so   that  no 
straight  joints  occur.     This  system  has  the   advan- 
tage of  being  particularly  simple,   only  necessitating 
the  use  of  the  one-standard  type  of  block  (Figs.  25 
and  36),  whilst  the  wall-thickness  separating  waste  gases 
and  secondary  air  is  reduced  to  3  inches   with   perfect 
immunity  from  short-circuiting. 

In  Drake's  system  rectangular  fireclay  tubes  (Fig.  37) 
are  employed,  the  waste  gases  travelling  backwards  and 
forwards  through  these,  whilst  the  secondary  air  traverses 
upwards  around  the  outside  of  the  tubes.  The  tubes  are 
placed  end  to  end,  all  joints  being  covered  by  bricks  for 
the  purpose  of  avoiding  by-passing.  If  through  the  movement  of  brickwork  by- 
passing does  take  place,  it  can  at  once  be  seen  and  remedied  through  the  front 
wall  of  the  regenerator.  This  is  done  by  means  of  a  "  paddle  "  and  patching 


Secondary  Air 


FIG.  34. — KLONNE  REGENERA- 
TOK  BLOCK. 


FIG.  35.  —  GIBBONS  & 
MASTERS'  REGENERA- 
TOR BLOCKS. 


FIG.  36. — GIBBONS  &  MASTERS'  REGENERATOR  SYSTEM. 


Secondary  Air 


Waste  Gases 


FIG.  38. — THE  PINTSCH  SYSTEM  OF  REGENERATION.     THE  CROSS  FLUES 
FIG.    37. — ARRANGEMENT    OF    DRAKE'S  ARE  FOR  SECONDARY  AIR,  AND  THE  LONGITUDINAL  FLUES  TAKE  THE 

PATENT  TUBULAR  REGENERATOR.  WASTE  GASES. 

69 


70 


MODERN   GASWORKS   PRACTICE 


Waste  Gases 


FIG.  39. — BROWN'S  REGENERATOR. 


individual  layers.  The  second- 
ary air,  in  an  ascending  stream, 
passes  outside  the  tubes  and 
through  the  cross-flues,  the 
waste  gases  travelling  down 
from  the  furnace  through  the 
tubes.  The  shaped  bricks  are 
rebated  at  their  ends,  thus 
avoiding  leakage  between  the 
flues. 

Brown's  patent  regenera- 
tor is  shown  in  Fig.  39. 
Ordinary  sized  firebricks  fit- 
ting into  rebates  in  the  special 
-tiles  are  used  for  staying  the 
vertical  walls.  In  building  the 
flues  the  "  bed  "  and  "  cross- 
joints  "  of  the  tiles  are  broken 
in  both  directions.  The  stay- 
ing bricks  do  not  extend  more 
than  half-way  through  the 
tiles,  so  that  in  the  event  of 
one  tile  breaking,  short-cir- 
cuiting does  not  take  place. 
Brooke's  system  (Fig.  40)  is 


material,  in  the  same  way  as  with  a 
cracked  retort.  As  regards  the  supply 
of  secondary  air,  each  vertical  section 
is  absolutely  distinct  from  inlet  to  out- 
let, therefore  under  control,  and  the 
quantity  at  any  point  along  the  length 
of  the  combustion  chamber  can  be  regu- 
lated at  the  secondary -air  inlet  slide. 

A  Continental  type  of-  regenerator 
is  shown  in  Fig.  38.  In  this  pattern 
the  walls  separating  the  hot  gases  and 
air  are  reduced  to  a  minimum  as  re- 
gards thickness,  and  special  tubular 
fireclay  bricks  are  employed.  These 
bricks,  placed  lengthwise  to  the  furnace, 
have  transverse  grooves  on  the  upper 
and  lower  outer  surfaces  and,  when  put 
together,  form  cross-flues  between  the 


PIG.  40. — BROOKE'S  REGENERATOR. 


THE  HORIZONTAL  RETORT  BENCH 


71 


another  in  which  contact  is  arranged  for  by  tubular  means.  It  differs  from 
types  given  in  Figs.  37  and  38,  however,  in  that  in  this  case  the  secondary  air 
travels  inside  the  tubes,  the  waste  gases  circulating  around  the  outside.  The 
ingoing  air  travels  backwards  and  forwards  in  a  zigzag  direction,  and  is  admitted 
at  two  places  on  each  side  of  the  furnace  front,  and  in  four  similar  places  at  the  back 
of  the  bench,  so  that  there  are  eight  inlets  in  all.  The  air  passing  through  the  various 
series  of  horizontal  flues  is  kept  entirely 
distinct  from  the  air  travelling  in  the  ad- 
joining series ;  thus  the  supply  to  the 
various  portions  of  the  combustion  cham- 
ber is  under  control.  The  waste  gases, 
after  leaving  the  setting,  pass  vertically 
downwards,  and  are  kept  in  separate 
streams  until  they  reach  the  bottom  of 
the  regenerator  flues,  when  they  enter  a 
common  channel.  At  the  bottom  of  each 
separate  compartment  a  damper  enables 
any  one  of  the  streams  to  be  controlled. 
In  the  illustration  given,  the  amount  of 
direct  contact  surface  between  the  waste- 
heat  and  the  secondary-air  flues  is  434 
square  feet. 

An  illustration  of  the  Winstanley  re- 
generator is  given  in  Fig.  41.  The  chief 
point  to  notice  about  this  type  is  that  the 
secondary  air  is  taken  in  in  two  distinct 
streams,  one  on  each  side  of  the  waste- 
gas  channel,  so  that  the  maximum  heat 
is  extracted  from  the  hot  products.  It 
will  be  noticed  that  the  inner  stream 
of  secondary  air  is  sandwiched  between 
the  waste  gases  and  the  producer,  whilst  primary  air  is  admitted  through  side 
channels. 

It  is  a  striking  fact  that  few  standard  English  settings  embrace  facilities  for 
heating  the  primary  air  as  well  as  the  secondary.  Such  systems  are  more  frequently 
met  with  on  the  Continent,  where  many  complicated  arrangements  are  introduced. 
From  an  analysis  of  fuel  results,  however,  it  appears  that  attention  to  the  practical 
points  of  design  is  of  greater  value  than  purely  theoretical  refinements. 

(/)  THE  GENERAL  ARRANGEMENT  or  THE  SETTING 

This  is,  in  the  first  instance,  entirely  dependent  upon  the  capacity  of  the  unit 
in  question.  Small  works  have,  of  course,  to  take  up  the  small  fluctuations  in 
demand  by  setting  down  units  of  varying  capacity.  Although  in  rare  instances  it 
is  done,  it  is  not  advisable  to  work  a  portion  of  an  arch  during  slack  periods,  as  fuel 


FIG.  41.- 


WlN  STANLEY  RETORT  SETTING,  SHOWING 
SYSTEM  OF  REGENERATION. 


72 

consumption  is  unavoidably  increased.  If,  however,  there  is  no  other  means  of 
regulating  the  output,  it  will  be  found  preferable  to  work  the  retorts  in  one  vertical 
row.  The  damper  on  this  side  of  the  setting  is  then  opened  and  that  on  the  opposite 
side  closed,  so  that  the  furnace  gases  are  pulled  around  those  retorts  in  operation. 
The  greater  the  number  of  retorts  to  a  bed,  the  lower  (pro  rata)  will  be  the  fuel 
consumption.  Hence  settings  of  twelve  have  come  into  fairly  extended  use.  One 
of  the  first  considerations — of  particular  moment  in  cases  where  land  is  expensive 
and  the  quantity  limited — is  the  productive  capacity  per  square  foot  of  area.  The 
highest  yield  in  this  respect  is  given  by  the  settings  of  ten  retorts  in  two  vertical 
rows — commonly  known  as  the  Bishop  of  London's  bench.  The  output  necessarily 
varies  with  the  size  of  retorts,  but  may  be  taken,  on  the  average,  as  200  to  250  cubic 
feet  per  diem  per  square  foot  of  ground  area.  This  figure  is  based  on  the  outside 
dimensions  of  the  retort  house  and  24  inches  X  16  inches  through  retorts.  For 
a  setting  of  8's  in  three  rows  the  capacity  would  be  reduced  to  150  to  180  cubic 
feet  per  diem  per  square  foot.  For  vertical  retorts  the  figure  (according  to  the 
system)  may  be  as  much  as  from  350  to  475  cubic  feet  per  square  foot. 

The  disposition  of  the  retorts  in  the  setting  must  be  such  that  the  heating  of 
each  one  is  as  uniform  as  possible.  In  settings  of  two  vertical  rows  this  is  more 
easily  assured  than  with  three  vertical  rows,  as  with  the  latter,  the  retort  immedi- 
ately above  the  combustion  chamber  has  to  face  the  fiercest  portions  of  the  flame. 
In  a  scientifically  constructed  setting  there  is  no  reason  why  the  average  tempera- 
ture of  any  of  the  retorts  in  that  setting  should  differ  by  more  than  150  °  Fahr. 

Under  all  circumstances  "  local  heating  "  must  be  avoided.  This  is  said  to 
be  taking  place  when  certain  defined  portions  of  the  setting  are  under  considerably 
greater  heat  than  the  remainder.  The  term  really  applies  to  the  differing  sections 
of  the  bench ;  for  instance,  we  do  not  speak  of  a  combustion  chamber  being  sub- 
jected to  local  heating  merely  because  its  temperature  is  greater  than  that  of  the 
remainder  of  the  setting.  If,  however,  one  section  of  this  chamber  were  consider- 
ably hotter  than  the  remainder,  the  hotter  section  would  be  giving  rise  to  local 
heating.  The  effects  of  this  derangement  are  very  often  seen  when  retort  doors 
are  opened — rings  of  dull  red  colour  encircle  the  retort  in  contrast  to  the  white 
heat  of  the  remainder.  This  is  indicative  of  bad  spacing  of  the  "  nostrils,"  or  of 
stoppage  of  one  or  more  of  these ;  but,  beyond  choking  up  by  dust  or  by  "  drip- 
pings "  from  the  upper  portion  of  the  bench,  the  cause  of  local  heating  can  usually 
be  attributed  to  constructional  defects  or  to  inferior  design.  The  following  con- 
siderations may  be  set  down  as  being  among  the  more  important  items  to  be  kept 
in  mind  when  designing  the  upper  portions  of  a  setting : — 

(1)  The  combustion  chamber  should  be  of  ample  size,  so  that  sufficient  space 
is  allowed  for  the  mixing  of  the  air  and  gas. 

(2)  The  "  nostril  holes  "  must  be  so  spaced  out  that  they  come  midway  between 
the  cross- walls  of  the  setting  and  the  combustion  chamber. 

(3)  The  air  and  producer  gas  should  not  come  together  too  closely,  and  should 
not  meet  at  right  angles.     The  effect  of  meeting  in  this  way  is  that  too  thorough 
mixing  takes  place,  and  short  flames  of  small  volume  are  the  result  (see  Fig.  42). 


THE  HORIZONTAL  RETORT  BENCH 


73 


FILLET    COMPOSED 

OF    &   BRICK    CUT 

DIAGONALLY 


FIG.  42. — DEFLECTING  SECONDARY  AIR  so  THAT  FURNACE 
GASES  MEET  IN  A  PARALLEL  DIRECTION.  DOTTED 
LINE  SHOWS  USUAL  POSITION  OF  CHANNEL  BLOCK. 


(4)  The  shape  of  the  nostrils  is  of  importance  ;  they  should  be  tapered  in  section 
(Fig.  42),  the  smaller  width  being  at  the  top.     In  this  way  any  lumps  or  dust  falling 
from  above  will  drop  through  the 

nostril  instead  of  lodging  in  it. 

(5)  The  secondary  air  on  both 
sides   of   the   setting   should   be 
under  dual  control  at   least,    or 
preferably    the    supply   to    each 
nostril  should  be  capable  of  regu- 
lation.     It  is   frequently    found 
that  the   air  has  a  tendency  to 
rush  towards  the  centre  nostrils 
of  the  furnace  arch,  this  giving 
rise    to  irregular  distribution    of 
heat  and  dull  mouth- pieces. 

(6)  The    "  nostrils  "    should  //\  W//A [ VX/X)(   V/ 

be  kept  low  in   comparison  with 

the  bottom  retorts.  If  they  are 
above  the  base  of  the  lowest  row 
of  retorts,  the  latter  will  be  in- 
sufficiently heated. 

(7)  For  settings  containing  two  vertical  rows  of  retorts  the  direction  of  dis- 
charge of  the  producer  gas  should  be  vertical  (Figs.  43  and  44).     For  three  rows  the 
"  nostrils  "   should  point  outwards.     In  this  way  more   effective   distribution  of 

heat  is  assured,  whilst  the  centre 
retort  is  not  subjected  to  a  direct 
cutting  heat. 

(8)  Retorts  are  far  less  liable 
to  "  local  heating  "  when  set  in 
tiers  of  two's.  Thus  if  a  setting 
of  eight  is  decided  upon  it  is  pre- 
ferable to  set  the  retorts  in  two 
vertical  rows  of  four  rather  than 
in  two  rows  of  three  and  one 
row  of  two.  In  addition,  the  for- 
mer arrangement  gives  a  greater 

yield  per  square  foot  of  ground  area.     The  chief  objection  is  that  if  hand  charging 

is  in  vogue  a  platform  will  have  to  be  used  for  the  top  tier. 

(9)  The  vertical  division  walls  supporting  the  retorts  need  not  be  of  greater  width 
than  4^  inches,  provided  that  9-inch  walls  are  put  in  where  the  retort  joint  comes. 
The  walls  forming  the  combustion  chamber  should  not  be  less  than  6  inches  in  width. 

(10)  The  gases  should  be  throttled  to  a  certain  extent  at  the  top  of  the  setting. 
These  get  away  too    quickly  if  excessive  room  is  permitted.     The  bottom  retorts 
should  be  no  more  than  4  inches  to  4|  inches  from  the  side  of  the  main  arch  wall. 


FIG.  43. 


FIG.  44. 


74 

SPECIFICATIONS  FOR  HORIZONTAL  BENCHES 

It  would  not  be  possible,  owing  to  the  multitude  of  designs  now  adopted  by 
individual  engineers,  to  give  here  a  general  specification  for  a  horizontal  retort- 
bench.  The  foregoing  pages  should,  however,  prove  of  some  assistance  to  the  engi- 
neer contemplating  extensions  or  renewals ;  and,  with  their  aid,  there  should  be 
little  difficulty  in  compiling  specifications  for  benches  of  whatever  type  or  capacity. 
The  chief  points  requiring  consideration  have  been  fully  dealt  with,  and  in  addition 
it  is  imperative  to  ensure  that  first-class  material  should  be  used  throughout.  The 
joints  should  be  thin,  and  two  to  one  cement  mortar  used  in  all  stock  brickwork, 
with  fireclay  cement  for  all  fireclay  work.  As  regards  the  types  of  materials  suitable 
for  various  portions  of  the  setting,  reference  should  be  made  to  Chapter  VI,  dealing 
with  Refractory  Materials. 

THE   COST  OF  HORIZONTAL  RETORT  SETTINGS 

Costs  of  erection  will  necessarily  vary  to  some  extent  in  accordance  with  the 
fluctuations  in  price  of  materials  and  labour,  also  the  design  or  "  stiffness  "  of  the 
work  put  down.  As  an  instance  of  the  latter  item  it  may  be  pointed  out  that  stage 
floors,  whilst  costing  on  an  average  about  £3  per  mouthpiece,  may  rise  to  as  much 
as  £8,  in  cases  where  exceptionally  heavy  charging  machinery,  etc.,  is  allowed  for. 
Other  factors  affecting  the  ultimate  cost  are  the  distance  and  ease  of  access  of  the 
point  of  supply  from  the  site  on  which  the  structure  is  to  be  erected,  also  the  pre- 
vailing railway  rates  and  water  freightage.  In  most  cases  all  the  above  considera- 
tions should  not  influence  the  following  prices  to  a  greater  extent  than  5  per  cent. 
in  either  direction.  Owing  to  competition  amongst  contractors,  a  certain  amount 
of  "  cheeseparing  "  is  inevitable  in  the  preliminary  tenders ;  for  this  reason  the 
figures  given  below  lean,  if  anything,  towards  extravagance — that  is  to  say,  they 
exemplify  expenditure  where  a  few  extra  pounds  have  not  been  withheld. 

No.  I 

• 

SETTINGS  OF  "  TENS."     Two  vertical  rows  of  5  retorts,  24  inches  x  16  inches  x  20  feet. 
Say  about  10  beds,  carbonizing  130  tons  per  diem. 

£     s.    d. 

Foundations  and  excavation,  for  bench  and  chimney  .          .          .200  per  mouthpiece. 

Arches,  spandrils,  main  flue        .       '  »  '       .         .     •    .          •         .900  ,, 

Buckstays  and  steel  bracing       .         .                   .          .                   .     2  10     0  ,, 

Chimney :  Brickwork,  £1  7s.  6d.  ;  bracing,  Is.  6d.                  .          .1150  „ 
Mouthpieces,  hydraulic  mains,  ascension  pipes  (both  ends  of  retort), 

and  all  retort  ironwork         .          ....          .          .          .   14     0     0  „ 

Tar  towers  (C.I.)  and  fittings      .•     •  w"        .        '..''.'.          .     0  15     0  „ 

Retort-house  governor  and  connexions         ;         ...         .          .     0  10    0  „ 

Retort  settings,  producers,  producer  ironwork,  etc.       .          .          .  20    0    0  „ 


£50  10    0    per  mouthpiece. 


i.e.  £80  per  ton  of  coal  per  maximum  diem. 

Or  £6  5s.  per  1,000  cubic  feet  of  gas  per  maximum  diem. 


THE  HORIZONTAL  RETORT  BENCH 


Bench  and  fittings  as  above     ....... 

Retort  house,  including  roof  and  foundations 

Stage  floors  :    Steelwork,  £3  ;   concrete  and  expanded  metal,  £1  10s. 

Tunnel  floors  .... 

Stoking  machinery    (say    "  F-A "    combined    machine,    coal    con- 
veyors, breakers,  elevators,  hoppers)     .... 

Electric  generating  plant    ...... 


£    s. 

50  10 

33     0 

4  10 

2     0 


30 
5 


0 

10 


d, 

0 

0 

0 

0 

0 

0 


per  mouthpiece. 


£125  10     0    per  mouthpiece. 

£200  per  ton  of  coal  per  maximum  diem. 
£12  \ls.  per  1,000  cubic  feet  per  maximum  diem. 

N.B.  —  It  should  be  explained  that  costs  for  horizontals  based  on  the  coal  used  are  extremely 
erratic,  and  by  manipulation  of  the  charges  and  the  use  of  more  coal  the  above  figure  could  be 
reduced  from  £200  to  £160. 

No.  II 

SETTINGS  OF  "  EIGHTS,"  in  three  rows,  22  inches  x  16  inches  x  20  feet  retorts. 
About  10  beds,  carbonizing  from  90  to  100  tons  per  diem. 


Foundations  and  excavations  for  bench  and  chimney  . 
Arches,  spandrils,  main  flue        ..... 

Buckstays  and  steel  bracing        .... 

Chimney  :   Brickwork,  £1  10s.  ;  bracing,  10*. 

Mouthpieces,  hydraulic  mains,  ascension  pipes  (both   ends   of   re- 
torts), foul  mains         ........ 

Tar  towers  and  fittings      ....... 

Retort  settings,  producers,  producer  ironwork,  etc. 


i.e.  about  £88  per  ton  of  coal  per  maximum  diem. 

No.  Ill 

HORIZONTAL   RETORT   SETTINGS.     Three  beds    of    "  Six  "—22  inches  x  16   inches  x  10   feet. 
Carbonizing  10  to  12  tons  of  coal  per  diem. 

£     s.    d. 
Foundations  and  excavations      .          .          .          .          .          .          .300    per  mouthpiece. 

Arches  and  spandrils.          .          .          .          .         .          .          .          .   12  10    0  „ 

Buckstays  and  steel  bracing        ...... 

Chimney  .         .         . 

Mouthpieces,  hydraulic  mains,  and  all  retort  ironwork 

Retort  settings,  producer,  and  producer  ironwork 

Tar  tower  and  fittings,  tar  main,  etc.          .... 


£    s. 
.     2    0- 
.   10    0 
.     2  10 
.     2    0 

.  14  10 

.     1     0 
.  21  10 

d, 
0 
0 
0 
0 

0 
0 
0 

per  mouthpiece. 

£53  10 

0 

per  mouthpiece 

300 

»> 

2  10    0 

»f    • 

13    0    0 

h 

21     0    0  ' 

n 

200 

»» 

£57    0    0    per  mouthpiece. 


i.e.  about  £95  per  ton  of  coal  per  diem. 


INCLINED   RETORT   SETTINGS 

Little  attention  need  be  given  to  inclined  retorts,  which  cannot  be  considered 
as  appertaining  to  modern  gasworks'  practice.  The  originator  of  the  system,  M. 
Coze,  designed  his  settings  with  the  retorts  set  at  an  angle  of  32°  with  the  horizontal 
—i.e.  the  theoretical  angle  of  repose  of  coal.  The  chief  merits  (also  largely  theoreti- 


76 


MODERN   GASWORKS   PRACTICE 


•cal)  were  the  absence  of  charging  and  discharging  machinery  and  the  wear  and 
tear  connected  with  this  apparatus,  also  only  one  ascension  pipe  was  employed, 
this  being  at  the  lower  end  of  the  retort.  Other  experimenters  have  worked  with 
the  retorts  at  various  angles  ranging  up  to  45°  ;  but  it  is  now  generally  recognized 
that  if  automatic  charging  is  to  be  carried  out  it  is  best  done  by  placing  the  retort 
•on  end. 

Inclined  retorts  are  seldom  entirely  automatic,  and  the  charge  has  invariably 


FIG.  45. — INCLINED  RETORT  SETTING. 

to  be  "started  on  the  run",  by  pricking  up  at  the  bottom  and  pushing  from  the 
top.  Moreover,  the  character  of  the  charge  is  materially  affected  by  the  kind,  size 
and  degree  of  dampness  of  the  coal  in  use.  "  Creeping  "  often  takes  place  during 
the  period  of  distillation,  with  the  result  that  the  upper  portions  of  the  retort  are 
completely  uncovered.  In  G.  R  Love's  system  the  retorts  were  set  at  45°  and 
received  full  charges,  two  ascension  pipes  being  provided.  The  system  has  now 
been  abandoned. 


THE  HORIZONTAL  RETORT  BENCH 


77 


With  regard  to  fuel  consumption,  inclined  systems  are  more  extravagant  than 
horizontals,  and  an  average  figure  of  16  Ib.  of  coke  per  100  Ib.  of  coal  carbonized 
(i.e.  22  per  cent,  of  the  coke  made  )  may  be  given. 

The  intricacy  of  this  type  of  setting  renders  it  more  costly  than  the  horizontal 
bench.  For  the  complete  setting,  inclusive  of  all  ironwork,  producers,  chimney, 
foundations,  etc.,  the  approximate  cost  per  mouthpiece  would  be  £65, 

OUTSIDE   PRODUCERS 

The  term  "  outside  "  or  "  external "  producer  embraces  those  types  which  do 
not  form  part  and  parcel  of  the  retort  bench ;  that  is  to  say,  the  producer  gas  is 
generated  at  some  distance  from  the  point  at  which  it  is  to  be  consumed.  Outside 
producers  as  now  employed  on  gasworks  may  be  classified  as  follows  : — 

1.  Coke-fired,     (a)  External  types,     (b)  Semi-external  types. 

2.  Coal  fired  (or  mixture  of  coke  and  coal),  with  plant  for  recovery  of  by- 
products. 

3.  High-pressure  producers. 

External  producers  of  all  types  are  entirely  confined  to  the  largest  of  gasworks. 
Although  they  cannot  compets  with  the  self-contained  furnace  on  the  score  of 
fuel  economy,  their  chief  recommendations 
lie  in  a  somewhat  reduced  capital  outlay,  if 
the  producer  is  of  a  simple  type,  compara- 
tively low  labour,  charges,  and  little  wear  and 
tear.  The  working  conditions  for  the  men  are 
also  better.  A  distinct  advantage,  moreover, 
is  the  finer  regulation  of  temperature  in  the 
settings  owing  to  the  possibility  of  passing 
the  gas  on  its  way  to  the  settings  through 
metal  cocks.  The  ordinary  coke-fired  exter- 
nal producer  is  very  similar  in  appearance 
and  construction  to  a  water-gas  generator, 
the  outer  casing  being  made  of  mild  steel 
plates,  with  a  lining  of  firebricks  and  thin 
layer  of  slag  wool.  In  all  cases  a  forced  air- 
blast  is  provided,  consequently  a  compara- 
tively fine  fuel  may  be  made  use  of.  One  of 
the  largest  installations  of  outside  producers  is  that  laid  down  at  the  Provan  works- 
of  the  Glasgow  Corporation,  some  ten  years  ago.  These  producers,  designed  on  the 
lines  of  that  shown  in  Fig.  46,  are  rectangular  (not  circular)  in  section,  and  twelve  of 
them  were  erected,  to  be  used  in  conjunction  with  sixty  beds  each  of  twelve  retorts. 
The  steel  casings  are  13  feet  3  inches  high  by  9  feet  4  inches  long  and  6  feet  4  inches 
wide,  and  are  lined  with  9  inches  of  firebrick  work,  with  a  2-inch  cavity  filled  in  with 
slag  wool.  The  gas  is  led  away  from  each  producer  by  a  lined  flue  casing  measuring 
2  feet  by  3  feet  6  inches,  this  passing  into  a  round  main  flue  pipe  of  4  feet  10  inches 
diameter.  Owing  to  the  forced  draught  made  use  of  with  this  type  of  producer  it  i& 


FIG.  46. — OUTSIDE  PRODUCER. 


78 


MODERN   GASWORKS   PRACTICE 


tave  been  producers  of  the  Mond  and  Kerpely  types, 
been  confined    to    Continental    works.       A  Mond   gas 


essential  that  an  effi- 
cient dust  chamber 
should  be  provided,  so 
that  the  gas  is 
thoroughly  cleansed 
before  reaching  the 
combustion  chambers 
of  the  settings.  In  the 
Pro  van  installation  the 
main  flue  is  inter- 
cepted by  dust  cham- 
bers measuring  22  feet 
high  by  11  feet  4 
inches  long  by  6  feet 
10  inches  wide. 

The  semi- external 
producers  embrace 
those  -types  which  are 
adjacent  to  (and  in 
some  "cases  portion  of) 
the  setting,  but  which 
are  of  larger  dimen- 
sions than  the  usual 
self-contained  p  r  o  - 
ducer,  and  supply  the 
requirements  of  two, 
or  perhaps  three,  set- 
tings. In  some  in- 
stances these  producers 
are  erected  on  either 
side  of  the  retort 
bench,  and  account  for 
the  heating  of  the  half 
portion  (on  the  side  on 
which  they  are  situ- 
ated) of,  say,  three 
settings. 

THE  MOND  PRO- 
DUCER. 

Among  the   more 

recent      introductions 

The  latter  have,  so  far, 

installation   was   erected 


THE  HORIZONTAL  RETORT  BENCH 


79 


at  the  Saltley  works  of  the  Birmingham  Corporation  in  1912,  for  the  purpose  of 
heating  a  battery  of  coke  ovens  for  the  carbonization  of  coal.  A  general  idea  of  the 
producer,  complete  with  apparatus  for  the  recovery  of  by-products,  is  shown  in  Fig. 
47,  whilst  a  section  of  the  generator  is  given  in  Fig.  48.  The  producer  may  be 
fed  with  a  mixture  of  coke  or  breeze  and  coal  slack,  and  is  capable  of  gasifying 
about  18  tons  of  these 
fuels  per  24  hours.  The 
Birmingham  plant  con- 
sists of  five  producers. 
The  base  of  each  is  sealed 
in  water,  into  which  the 
ash  descends,  this  being 
periodically  removed 
without  interfering  with 
the  process  of  gas-mak- 
ing. The  producers  can, 
if  desired,  be  fitted  with 
automatic  ash-removing 
apparatus.  A  "  wet  " 
air-blast  is  blown  through 
the  fuel-bed  by  means  of 
Roots'  blowers,  and  in 
this  way  the  temperature 
is  maintained  at  a  com- 
paratively low  point,  so 
that  ash  alone,  and  no 
clinker,  is  formed.  The 
quantity  of  steam  intro- 
duced with  the  air-blast 
amounts  to  about  2|  tons 
for  every  ton  of  fuel  gasi- 
fied, when  ammonia  is 
recovered,  the  low  tem- 
perature thus  ensured 
preventing  the  splitting 
up  of  the  ammonia,  and 

accounting     for     nearly  FlG>  48._ MOND  PRODUCER. 

four    times     the     yield 

obtained  from  the  ordinary  gasworks  process  of  distillation.  The  supply  of  steam 
and  air  before  entering  the  producer  traverses  a  regenerator  (in  which  it  derives 
heat  from  the  outflowing  producer  gas),  and  afterwards  the  annular  space  formed 
round  the  inner  shell  of  the  producer  by  the  external  casing.  On  leaving  the  pro- 
ducer and  regenerator  the  gas  passes  to  a  mechanical  washer,  where,  by  means  of 
a  water  spray  formed  by  quickly  rotating  dashers,  tar  and  dust  are  eliminated. 


80 


MODERN   GASWORKS   PRACTICE 


Ammonia  is  then  recovered  by  washing  in  a  special  tower  with  an  acid  solution, 
sulphate  of  ammonia  being  recovered  direct,  and  the  gas  is  finally  treated 
in  cooling  towers  and  centrifugal  fans  for  the  removal  of  the  last  traces  of 
tar. 

In  the  case  of  large  installations  of  Mond  gas  plants  about  150,000  cubic  feet 
of  gas,  costing  \d.  per  1,000  cubic  feet,  can  be  obtained  from  a  ton  of  coal  slack. 
The  calorific  power  of  the  gas  is  about  140  B.Th.U.  per  cubic  foot.  With  regard  to 
comparative  costs  of  heating  by  Mond  gas  and  by  means  of  the  ordinary  coke- 
fired  regenerator  furnace,  Mr.  W.  Chaney  has  given  the  following  figures  : — 


COST  OF  HEATING  RETORTS  BY  REGENERATOR  FURNACES.     BASED  ON  A 
CONSUMPTION  OF  12  PER  CENT.  OF  THE  WEIGHT  OF  COAL  CARBONIZED 


Coke  at  14s.  per  ton 

Labour    .          , 

Repairs  and  depreciation. 

Total  cost  of  heating 


20-2d.  per  ton  of  coal  carbonized. 
2-7d. 
1-Od. 

23-9d.  (say  2s.)  per  ton  carbonized. 


COST  OF  HEATING  BY  MOND  GAS 


(a)  All  coal  slack.     (Compressed  Coal  in  Chamber  Ovens.     See  p.  182.) 

Small  coal  at  10s.  per  ton       .  .  .  , 

Boiler  fuel        .          .          .          ,  •  .   .  , 

Labour    .         ,                   ,          ,  ,  . 

Repairs  and  depreciation           .  "      .  , 

Oil,  etc.  .         .         .         .         ..  .  '. 

Sulphuric  acid,  at  30s.  per  ton  ,  , 

Sulphate  bags,  packing     .       •»  „.  ,  - 


Gross  cost          .          ,        . ,          .         , 
Less  sale  of  sulphate         . 

Net  cost  of  heating 

(b)  Mixture  of  half  coal  slack  and  half  coke  dust. 

Small  coal  at  10s.  per  ton 

Coke  dust  at  Is.  6rf.  per  ton    . 

Boiler  fuel        .          .          .    •      . 

Labour    .          .          .          .          .         ,.          . . 

Repairs  and  depreciation  .          . 

Oil,  etc •.       '  . 

Sulphuric  acid,  at  30s.  per  ton 
Sulphate  bags,  packing     .          . 

Gross  cost          .         .       V  '  ; 

Less  sale  of  sulphate         ."        -.'         .          4 


18-Od.  per  ton  of  coal  carbonized. 
2-15d. 
3-84d. 
8-53d. 
0-34d. 
l-Q5d. 


35-27^.  per  ton  of  coal  carbonized. 
18-Sld.  „  „ 


.  per  ton  of  coal  carbonized. 


9-Orf.  per  ton  of  coal  carbonized. 


0-30d. 


26-81d.  per  ton  of  coal  carbonized. 
l2-52d. 


Net  cost  of  heating 


14-29^.  per  ton  of  coal  carbonized. 


THE  HORIZONTAL  RETORT  BENCH 


81 


THE   KERPELY  HIGH-PRESSURE   PRODUCER 

The  Kerpely  high-pressure  producer  (Fig.  49)  is  now  at  work  in  conjunction 
with  retort  settings  or 
chamber  ovens  at  many 
large  Continental  gasworks, 
including  Vienna,  Berlin, 
and  Paris.  The  chief  fea- 
ture about  its  design  is  a 
revolving  grate,  by  means  of 
which  the  clinker  as  it  is 
formed  is  ground  up  and 
thrown  outside  the  pro- 
ducer. The  producer  is 
primarily  employed  on  ac- 
count of  its  ability  to  gasify 
extremely  low-grade  and 
dusty  fuels  —  practically 
waste  materials  having  a 
calorific  power  as  low  as 
5,000  B.Th.U.  per  Ib.  As 
in  the  Mond  system,  air  and 
steam  are  supplied  to  the 
producer,  in  this  case  up  to 
a  pressure  of  30  inches  of 
water.  The  lower  portion 
of  the  shell  is  water- 
jacketed,  which  precludes 
the  adhering  of  clinker  to 
the  side  walls.  In  a  recent 
trial  run  with  pan  coke 
having  a  calorific  power  of 
10,500  B.Th.U.  per  Ib.,  the 
gas  produced  was  found  of 
the  following  average  com- 
position : — 


FIG.  49. — KERPELY  HIGH-PRESSURE.  PRODUCER.. 


Carbon  dioxide  . 
Carbon  monoxide 
Hydrogen 


7-9  per  cent. 
234 
12-5 


The  calorific  power  of  the  gas  was  115  B.Th.U.  per  cubic  foot.  The  high- 
pressure  Kerpely  producers  are  now  made  in  two  standard  sizes,  the  largeu  appa- 
ratus being  8  feet  6  inches  in  diameter,  22  feet  high  over  all,  and  having  a.  fuel 
consumption  of  from  14  to  16  tons  per  twenty-four  hours.  Twenty- four  of  these 
producers  are  now  at  work  on  the  Vienna  gasworks. 


82  MODERN   GASWORKS   PRACTICE 

LOSS   OF   HEAT   BY   RADIATION 

In  connection  with  the  loss  of  heat  due  to  radiation  from  the  conduits  of  outside 
producers,  Butterfield  has  pointed  out  that  if  the  producer  stands  at  some  distance 
from  the  setting,  and  the  gas  has  to  travel  through  long  pipes  before  reaching  the 
furnaces,  or  if  it  is  stored  for  a  short  time  in  a  gasholder,  then  17  per  cent,  of  the 
heating  value  of  the  fuel  will  be  more  or  less  completely  lost.  This  amount 
of  loss  represents  the  heat  which  is  expended  in  raising  the  producer  gas  to  the 
temperature  at  which  it  leaves  the  furnace.  With  regard  to  the  methods  of 
insulation  employed  for  maintaining  the  producer  gas  at  the  highest  possible  tem- 
perature, the  author  thinks  that  the  researches  of  Neumann  on  the  reaction  between 
gases  after  contact  with  solid  heated  carbon  have  never  been  considered  in  conjunction 
with  the  working  of  outside  producers  of  whatever  type.  Neumann  has  shown  that 
at  the  furnace  outlet  there  is  a  lower  percentage  of  carbonic  monoxide  and  a  higher 
percentage  of  carbon  dioxide  in  the  gas  than  at  the  surface  of  the  fuel,  and  that  the 
total  combustibles  are  less  in  percentage  at  the  outlet  than  at  a  point  just  above  the 
top  of  the  fuel  bed.  It  is  further  pointed  out  that  the  change  in  composition  of  the 
gas  after  leaving  the  fuel  bed  can  be  avoided  by  using  an  outlet  pipe  which  is  quickly 
cooled  by  means  of  a  jacket  through  which  cold  water  is  circulated.  From  these 
researches  it  would  appear,  then,  that  the  gas  derived  from  producers  of  the  outside 
type  is  extremely  likely  to  deteriorate  in  quality  to  some  extent  during  its  passage 
along  the  comparatively  long  length  of  gas  pipe  ;  and,  what  is  more,  the  deterioration 
is  likely  to  be  augmented  by  the  methods  commonly  adopted  for  the  prevention  of 
radiation.  The  question  at  issue,  however,  is  as  to  whether  the  greatest  heat  economy 
would  be  entailed  by  cooling  the  gas  immediately  it  leaves  the  producer,  and  thus 
checking  the  further  oxidation  of  CO  to  C02,  or  whether  the  conservation  of  sensible 
heat  due  to  the  lagging,  etc.,  is  desirable  even  at  the  expense  of  an  inferior  quality  of 
gas. 

Outside  producers,  with  the  exception  of  the  semi- external  types,  are  always 
fed  with  cold  coke,  this  accounting  for  additional  thermal  losses,  unless  the  sensible 
heat  in  the  coke  as  it  leaves  the  retort  is  utilized  (as  in  some  vertical  retort  systems). 
When  the  cold  coke  is  charged  into  the  producer  it  should  be  as  free  from  moisture 
as  possible,  otherwise  this  will  be  driven  off  in  the  form  of  steam,  which  passes  on  to 
the  settings.  In  some  forms  of  external  producer  the  furnace  gases  are  taken  off  at 
a  point  slightly  below  the  average  fuel  level,  so  that  any  steam  formed  will  be  split 
up  by  passage  through  the  hot  coke. 


CHAPTER    IV 
THE   CONTROL   OF   HORIZONTAL   RETORT   SETTINGS 

THE  problem  of  the  starting- up,  working,  and  regulation  of  retort  bench  producers 
is  one  with  which  the  gas  engineer  is  continually  face  to  face  ;  and  there  are  few  more 
trying  ordeals  than  that  of  warming-up  to  present-day  heats,  and  afterwards  main- 
taining such  heats  with  regularity.  First,  it  has  to  be  realized  that  in  the  case  of 
new  work,  or  settings  which  have  previously  been  in  use,  but  have  been  let  down, 
the  range  of  temperature  through  which  they  have  to  be  raised  is  as  much  as  2,000° 
Fahr.,  when  considering  the  retorts,  and  about  600°  higher  as  far  as  the  combustion 
chamber  and  its  immediate  surroundings  are  concerned.  Hence,  if  damage  is  to  be 
avoided,  more  than  ordinary  care  must  be  given  to  the  procedure  known  as  "  slow 
fires."  Rapid  temperature  rises  are  the  sure  forerunners  of  cracks  and  opening 
joints,  whilst  particular  attention  is  essential  with  many  of  the  modern  forms  of 
regenerators  designed  on  elaborate  lines  for  bringing  about  an  interchange  of  heat 
between  the  waste  gases  and  secondary  air. 

"SLOW  FIRES" 

With  regard  to  picking-up  benches  from  cold,  there  is  a  prevailing  tendency  to 
hurry  the  work  along,  which  no  doubt  accounts  in  no  inconsiderable  way  for  the 
reduced  life  of  retorts,  etc.,  of  which  complaint  is  so  frequently  heard.  The  actual 
period  of  "  slow  fires  "  varies  to  some  extent  with  the  condition  of  the  setting  ;  that 
is,  whether  the  brickwork  is  "  green  "  throughout,  or  whether  the  bench  has  merely 
been  let  down  for  repairs.  In  the  former  case,  an  inflexible  rule  should  be  made 
that  "  slow  fires  "  must  continue  for  at  least  six  weeks.  This  period  may  be  reduced 
by  half  in  the  case  of  settings  which  have  previously  been  under  fire.  At  the  end 
of  this  time  the  fire  should  be  very  gradually  increased  over  a  period  of  about  three 
days  to  the  full  working  pitch  (i.e.  "  fast  fires  "),  which  must  be  continued  for  three 
or  four  days  before  the  retorts  are  charged  with  coal.  The  procedure  adopted  for 
manipulating  the  various  dampers  and  slides  during  preliminary  heating  and  picking- 
up  varies  in  accordance  with  the  taste  of  the  individual ;  but,  speaking  generally, 
the  following  points  are  those  chiefly  requiring  attention  in  connection  with  the  larger 
types  of  regenerator  settings.  First,  with  "  slow  fires  "  it  is  very  usual  to  isolate 
the  main  flue  and  chimney  during  the  earlier  portions  of  the  period,  this  being  done 
by  closing  the  main  dampers  between  the  regenerators  and  the  flue.  An  outlet 
for  the  warm  products  of  combustion  is  then  made  by  removing  a  brick  from  the 

83 


84  MODERN   GASWORKS   PRACTICE 

front  wall  of  the  setting  at  a  point  just  beneath  the  crown  of  the  furnace  arch.  In 
this  way  the  waste  gases  are  circulating  in  the  setting  alone.  In  addition,  of  course, 
it.  must  be  remembered  that  the  furnace  charging  hole  is  left  uncovered.  With 
regard  to  the  admission  of  air  to  the  furnace,  most  engineers  prefer  to  open  the  primary 
slides  only,  keeping  the  secondary  slots  tightly  sealed.  This  practice  is  certainly  to 
be  preferred,  for  then  less  risk  of  explosion  is  incurred  ;  but  at  any  rate  the  amount 
of  primary  air  required  will  be  trifling  in  comparison  with  that  necessary  for  full 
work,  and  usually  one-tenth  of  the  quantity  is  ample  for  maintaining  the  fire  at  the 
desired  pitch.  During  this  time  the  fire-bars  should  be  water-cooled  in  the  usual 
way,  and  clinkering  carried  out  about  twice  per  week.  As  regards  the  retorts,  the 
doors  of  these  should  be  closed,  so  as  to  retain  as  much  heat  as  possible ;  but  they 
should  on  no  account  be  tightened  up  with  the  levers,  otherwise  the  expanded  air 
and  steam,  being  unable  to  escape  (the  foul-main  valve  being  closed),  will  force  an 
exit  through  some  weak  spot  in  the  joints,  thus  giving  unnecessary  trouble  when  the 
retorts  are  charged  up.  Particular  attention  should  be  given  to  this  point  when 
new  work  throughout  is  being  dealt  with. 

"FAST   FIRES" 

When  the  time  comes  for  working  up  from  "  slow  "  to  medium  fires  certain 
precautions  are  necessary.  First,  the  main  flue  and  chimney  are  brought  into 
play  ;  and  to  this  end  the  setting  dampers  may  be  opened  to  a  small  extent  (usually 
about  one- quarter  of  their  full  working  amount),  but  the  outlet  made  in  the  front 
wall  of  the  setting  must  at  the  same  time  be  sealed  by  replacing  the  brick  which  was 
removed  at  the  outset.  In  some  instances  it  is  usual  to  open  the  main  dampers  to 
nearly  their  full  working  extent  for  an  hour  or  so,  in  order  to  heat  up  the  shaft  suffi- 
ciently to  ensure  its  creating  a  good  draught.  From  the  point  of  view  of  the  brick- 
work, however,  this  is  not  to  be  advised,  and  the  better  practice  is  to  keep  a  coke 
bucket  burning  for  some  few  days  at  the  base  of  the  chimney.  A  special  brick  panel 
or  cast-iron  door  should  always  be  left  in  the  chimney  for  this  purpose.  When 
working  medium  fires  the  furnace  lid  is,  of  course,  sealed  up  and  secondary  air 
admitted.  The  necessity  for  exercising  a  certain  amount  of  vigilance  before  doing 
this  is  dealt  with  later.  When  the  "  fast  fires  "  are  commenced,  the  dampers  and  air 
slides  may  be  adjusted  to  the  maximum  amount  required  for  working  the  setting. 

GENERAL  WORKING  POINTS 

There  is  little  doubt  that  the  trained  eye  is  by  far  the  most  effectual  judge  as 
to  the  manner  in  which  the  furnaces  are  doing  their  work.  Systematic  analyses 
are,  no  doubt,  helpful  so  far  as  the  prevention  of  waste  is  concerned,  but  their  chief 
drawback  is  that  whilst  giving  an  indication  of  the  quality  of  the  producer  gas  they 
entirely  neglect  the  equally  important  consideration  of  quantity.  This  accounts 
for  the  somewhat  common  experience  of  a  scientifically  perfect  gas  giving  decidedly 
indifferent  heats.  As  a  preliminary,  the  most  satisfactory  method  of  adjusting  the 
slides  is  to  increase  the  primary  supply  until  the  best  results  are  noticed,  thus  adopt.- 
ing  a  trial  and  effect  policy.  Having  hit  upon  the  correct  adjustment,  the  secondary 


CONTROL   OF  HORIZONTAL   RETORT   SETTINGS        85 


slides  are  regulated  until  the  characteristic  blue  flame  of  carbonic  oxide  is  seen  burn- 
ing at  the  ports  connecting  the  regenerators  with  the  waste-gas  flue.  This  indicates 
that  the  air  entering  through  the  inspection  plug  is  burning  the  unconsumed  CO. 
Such  a  state  of  affairs  is,  of  course,  wasteful,  and  the  secondary  ports  must  be  further 
opened  until  the  blue  flame  disappears.  Sufficient  quantities  of  oxygen  for  the 
combustion  of  the  carbon  monoxide  are  now  entering  the  setting ;  but  in  order  to 
ensure  a  slight  excess  the  secondary  slides  should  be  further  opened  to  a  small  extent, 
say  about  one-tenth  of  their  amount  at  the  time.  In  doing  this,  however,  judgment 
must  be  exercised  ;  for  an  additional  quantity  of  secondary  air  means  an  increased 
volume  of  waste  products,  hence  reduced  combustion  temperature.  ' 

WORKING  UNDER   PRESSURE 

Within  comparatively  recent  years  the  prevailing  fashion  was  to  work  the  retort 
bench  under  a  slight  vacuum  throughout  the  whole  of  the  setting.  It  is  now  recog- 
nized, however,  that  more  effective  results  are  ensured  by  maintaining  a  pressure 
in  certain  portions  of  the  bed.  If  possible,  an  endeavour  should  be  made  to  obtain 
a  slight  pressure  in  the  combustion  chamber,  and  this  will  depend  to  a  large  extent 
upon  the  position  of  the 
waste-gas  damper.  The 
latter  should  be  opened  to 
the  least  possible  extent, 
and  if  adjustment  must  be 
made  the  primary  slides 
should  be  turned  to,  when 
by  further  opening  them 
matters  will  be  improved, 
owing  to  the  velocity  of  air 
through  the  fuel  bed  being 
reduced.  All  producers  are, 
unfortunately,  affected  to 
no  little  extent  by  the  vary- 
ing conditions  of  the  fire, 
such  as  clinkering,  "  prick- 
ing-up,"  fluctuation  in  depth  of  fuel  bed,  etc.  ;  but  the  introduction  of  the  auto- 
matic damper  slide  (such  as  Brooke's)  has  gone  some  way  towards  remedying  this 
annoyance.  The  objects  of  such  slides  are  : — 

(a)  To  reduce  fuel  consumption. 

(6)  To  maintain  a  more  regular  temperature  in  furnace  and  setting. 

(c)  To  avoid  excessive  formation  of  clinker. 

The  apparatus  (Fig.  50)  consists  of  a  vane  A  attached  to  a  rod  on  which  moves 
an  adjustable  balance  weight  C.  The  vane  is  supported  from  two  small  hook  bolts 
on  which  it  swings.  A  flat  spring  E  presses  on  the  spindle,  the  intensity  of  the 
pressure  being  regulated  by  the  adjustable  screw  F.  There  is  also  provided  a  damper 
plate  H  for  use  when  shutting  down,  and  a  shield  piece  G.  The  regulators  are  made 


M-  C 


FIG.  50. — BROOKE'S  AUTOMATA  DAMPEE. 


86  MODERN   GASWORKS   PRACTICE 

to  fit  into  existing  secondary-air  flues,  or  to  bolt  on  to  the  front  of  clinkering  doors 
for  the  regulation  of  primary  air.  The  fuel  saving  by  the  introduction  of  these  slides 
has  been  shown  in  certain  cases  to  be  about  3  Ibs.  of  coke  per  100  Ibs.  of  coal 
carbonized. 

A  similar  type  of  regulator  is  also  made  for  use  with  chimney  shafts,  which, 
owing  to  variations  in  atmospheric  conditions,  account  for  considerable  fluctuations 
in  draught.  In  this  case  the  swing  damper  is  balanced  by  means  of  a  counterweight 
until  it  is  just  closed,  when  the  desired  draught  is  given.  Any  alteration  of  the  main 
damper  will  then  be  accompanied  by  a  movement  of  the  regulator,  which  will  open 
and  admit  cold  air  until  the  draught  is  reduced  to  the  set  amount.  Variations  due 
to  atmospheric  conditions  will  be  similarly  counteracted. 


A  word  is  necessary  here  with  regard  to  the  manner  in  which  tests  on  settings 
are  made.  When  drawing  off  samples  of  waste  gases  it  is  advisable  not  to  make 
use  of  the  bottom  or  damper  section  of  the  regenerator  for  the  purpose,  as  misleading 
analyses  may  be  the  outcome,  owing  to  the  by-passing  of  the  secondary  air.  In 
many  regenerator  settings  it  is  quite  common  to  find  that  the  vacuum  in  the  secondary- 
air  and  waste-gas  flues  is  practically  equal,  which  is  commendable  as  far  as  short- 
circuiting  and  by-passing  are  concerned.  When  such  is  the  case,  however,  it  rarely 
occurs  to  those  responsible  to  analyze  the  ingoing  secondary  air  at  a  section  near 
the  top  of  the  regenerator. 

A  point  worth  noticing  with  regard  to  regenerators  which  show  signs  of  serious 
short-circuiting  is  that  of  isolating  the  defective  sections  by  transposing  the  air-box 
to  a  position  higher  up  in  the  tiers  of  the  regenerator.  A  certain  amount  of  regenera- 
tion is,  of  course,  sacrificed  ;  but  usually  the  loss  is  more  than  balanced  by  the  restric- 
tion of  the  short-circuiting.  This  alternative  should  only  be  turned  to  when  repairs 
to  the  lower  sections  are  impossible.  Here,  again,  the  engineer  must  be  thoroughly 
conversant  with  the  constructional  details  of  his  setting  ;  for,  in  more  than  one  type 
of  regenerator,  the  raising  of  the  secondary- air  inlet  in  this  way  would  completely 
cut  off  the  secondary  supply  to  many  of  the  nostril  holes.  In  connection  with  these 
systems,  the  advantages  accruing  from  the  multiple  regulation  are  undoubtedly 
significant,  for  there  is  frequently  a  tendency  for  the  rush  of  air  to  be  greatest  towards 
the  centre  nostrils  of  the  furnace  arch.  This  entails  irregular  distribution  of  heat 
and  dull  mouthpieces.  With  the  separate  adjustments,  however,  the  mouthpiece 
temperature  is  well  under  control. 

As  regards  the  regulation  of  waste-gas  flue  draught  it  is  as  well  to  provide  two 
dampers  to  each  regenerator,  as  shown  in  Fig.  51.  The  upper  damper  can  then  be 
regulated  until  the  best  results  are  given,  while  during  temporary  stops  or  clinker- 
ing  the  lower  damper  is  brought  into  play.  The  latter  can  then  be  opened  again 
to  its  fullest  extent,  and  the  draught  is  governed  as  originally  by  the  upper  damper, 
which  has  not  been  moved.  Care  must  be  taken,  however,  to  see  that  the  lower 
damper  is  properly  sealed,  otherwise  air  will  be  drawn  past  it,  and  the  chimney 
draught  on  the  setting  correspondingly  reduced. 


CONTROL   OF  HORIZONTAL   RETORT   SETTINGS        87 

It  may  be  mentioned  here  that  in  the  ordinary  way  the  draught  on  the  chimney 
of  a  regenerator  setting  should  not  exceed  from  ^  to  Tf!0  inch  of  water.    The  actual 
vacuum    is    usually    measured  by  a  special 
direct-reading  instrument,  the  connecting  pipe 
of  which  is  thrust  into  the  sight  box  at  the 
base  of  the  chimney.     It  is  usual  to  calibrate 
these  instruments  in  hundredth  parts  of  an 
inch,  so  that  for  correct  working  the  indicator 
points  to  between  30  and  60.     Some  engineers 

prefer  to  employ  a  recording  gauge,  so  that  a 

,.  j  •     ,    i  FIG.  51. — DOUBLE  DAMPER  CONTROL. 

continuous  record  is  taken. 


RETORT-BENCH   EXPLOSIONS 

Though  serious  damage  resulting  from  the  explosion  of  producer  gas  in  retort 
settings  is,  fortunately,  rarely  met  with  on  gasworks,  it  is,  perhaps,  surprising  that 
this  is  the  case,  considering  the  singularly  small  amount  of  attention  which  is  often 
given  to  the  matter.  The  infrequency  of  these  explosions  is  partly  due  to  the  fact 
that  a  large  element  of  luck  enters,  into  the  question,  *  but  chiefly  because  they  are 
only  likely  to  occur  during  the  period  when  newly  constructed  settings  are  under 
"  slow  fires,"  or  when  benches  are  being  picked  up  again  for  work.  Mishaps  of  the 
kind,  however,  are  particularly  to  be  guarded  against ;  for,  in  addition  to  endangering 
the  limbs  of  those  members  of  the  retort-house  staff  who  may  be  in  the  vicinity  of 
the  bench  at  the  time,  the  resulting  damage  to  the  structural  work  of  the  setting 
may  be  considerable,  entailing  extensive  rebuilding,  and,  consequently,  expense. 

It  is  somewhat  puzzling  to  account  definitely  for  the  actual  source  of  explosions 
of  this  nature,  but  in  the  greater  number  of  instances  it  would  seem  probable  that 
a  mixture  of  carbon  monoxide  and  oxygen  finds  its  way  into  the  setting  at  a  time  when 
the  prevailing  temperature  is  insufficient  to  bring  about  its  ignition.  What  has  to 
be  recognized,  of  course,  is  that  during  the  time  when  a  setting  is  undergoing  its 
preliminary  heating  up  prior  to  being  put  into  full  work,  the  gaseous  firing  principle 
of  the  furnace  is  not  brought  into  play,  and  the  fuel  is  burnt  merely  as  in  the  old 
type  of  "  direct  "  fire.  That  is  to  say,  a  certain  amount  of  primary  air  is  admitted, 
the  object  being  to  burn  the  fuel  to  carbon  dioxide  in  the  furnace,  and  not  in  two 
steps,  as  is  eventually  to  be  done.  If  this  could  be  ensured,  then  an  incombustible 
gas  would  alone  be  circulating  in  the  setting ;  but  what  usually  takes  place  is  that 
the  primary  air  during  its  passage  through  the  shallow  bed  of  fuel  is  only  partially 
converted  into  CO  2,  whilst  some  CO  is  afterwards  formed.  At  the  same  time  air  may 
pass  through  (particularly  if  the  fuel  bed  is  very  uneven)  entirely  unchanged.  Thus  we 
have  a  mixture  of  CO  and  oxygen  travelling  throughout  the  setting.  The  general 
practice  adopted  during  "  slow  fires  "  is  to  shut  off  the  secondary  air  slides  com- 
pletely ;  but  in  some  cases  it  is  preferred  to  admit  a  small  supply  through  these  ports, 
for  it  is  claimed  that  in  this  way  a  better  draught  is  created,  which  ensures  the  more 
thorough  removal  of  steam  from  new  brickwork,  etc.  If  secondary  air  is  admitted, 


88 

however,  it  certainly  adds  to  some  extent  to  the  possibilities  of  an  explosion  in  the 
.setting  itself. 


^Explosions  of  producer  gas,  both  minor  and  severe,  are  usually  the  outcome  of 
^carelessness  on  the  part  of  the  man  responsible  for  the  supervision  of  the  settings, 
or  are  due  to  the  non-observance  of  certain  practical  rules  which  have  come  to  be 
recognized  as  the  result  of  everyday  experience.  The  most  probable  cause  to  which 
the  trouble  can  usually  be  traced  is  that  of  sealing  up  the  furnace  charging  door 
before  the  setting  has  reached  a  sufficient  degree  of  heat.  Some  explanation  of 
this  possibility  is,  perhaps,  necessary. 

First,  when  the  charging  hole  is  uncovered  any  CO  resulting  from  the  com- 
bustion of  the  fuel,  instead  of  travelling  onwards  through  the  nostrils  and  thence 
into  the  setting,  will  merely  pass  outwards  into  the  retort  house,  where  it  will  soon 
be  carried  away.  If,  however,  the  lid  is  replaced  over  the  charging  aperture,  the 
combustible  gas  must  necessarily  find  an  outlet  by  travelling  through  the  setting ; 
thus  the  latter  is  filled  with  an  explosive  mixture.  No  harm  may  come  of  this  for 
a  time,  but  as  the  temperature  of  the  setting  rises  the  ignition  point -of  the  gas  is 
reached,  when  explosion  occurs.  The  magnitude  and  force  of  the  explosion  depend, 
of  course,  upon  the  volume  of  the  combustible  mixture  which  is  circulating  in  the 
setting  at  the  time. 

Practical  experience  with  the  type  of  setting  in  question  is  really  the  most 
reliable  guide  as  to  when  the  state  of  affairs  is  safe  for  the  furnace  lid  to  be  put  in 
place.  Usually  it  is  merely  sufficient  to  be  satisfied  that  the  furnace  arch  is  just 
nicely  red-hot,  although  more  careful  individuals  go  so  far  as  to  say  that  the  bottom 
retorts  should  be  at  a  dull  red  heat.  The  latter  practice,  however,  is  conducive 
to  decided  extravagance  in  fuel.  But  whichever  method  is  adhered  to,  the  chief 
object  is  to  ensure  that  any  carbon  monoxide  and  oxygen  which  may  be  passing 
through  the  furnace  will  be  ignited  on  arriving  at  the  furnace  arch,  instead  of 
finding  its  way  into  the  setting. 

CHARGING  WITH  WET  COKE 

In  addition  to  the  charging- lid  danger,  other,  but  less  hazardous,  risks  are  run 
by  filling  up  the  furnace  with  decidedly  wet  coke,  or  by  charging  in  an  excessive 
quantity  of  cold  coke  at  a  time.  In  fact,  the  use  of  wet  fuel  should  always  be  avoided  ; 
for,  lying  in  a  stagnant  layer  on  the  surface  of  the  hotter  fuel,  it  permits  the  passage 
through  the  bed  of  carbon  monoxide  and  oxygen,  whilst  the  actual  flames  are  choked 
and  subdued,  and  the  temperature  of  the  upper  portions  of  the  furnace  is  reduced  for 
the  time  being.  The  result  is  that  the  inflammable  gas  is  not  burned  in  the  furnace, 
and,  circulating  throughout  the  setting,  it  is  eventually  ignited  when  the  heat  of  the 
fuel  picks  up,  and  the  flames  have  broken  through.  Precisely  the  same  argument 
applies  to  the  use  of  cold  coke,  which,  if  used,  should  only  be  introduced  in  com- 
paratively small  quantities  at  a  time.  By  far  the  best  practice,  however,  is  to  use 
nothing  but  red-hot  fuel  from  the  nearest  bench  which  happens  to  be  in  full  work. 


CONTROL   OF   HORIZONTAL  RETORT   SETTINGS        89 

TEMPORARY  STOPS 

On  the  majority  of  the  larger  gasworks  it  is  now  quite  the  general  practice  to 
discontinue  the  make  of  gas  for  a  certain  period  on  Sundays  ;  for  by  so  doing  the 
retort- house  hands  are  assured  of  a  well- earned  weekly  rest;  whilst  in  many  companies 
it  is  the  custom  to  pay  double  rates  between  6  a.m.  and  6  p.m.  on  this  day.  Hence 
the  temporary  stop  entails  some  fairly  considerable  saving  in  carbonizing  expenditure. 

As  a  general  rule,  the  stafT  of  a  gasworks  is  not  called  upon  to  attend  on 
Sunday,  thus  the  operations  of  discontinuing  carbonization  and  restarting  it  are 
practical  problems  with  which  many  gas  engineers  are  more  or  less  unfamiliar.  On 
first  thoughts,  the  procedure  would  not  appear  to  demand  any  exceptional  amount 
of  attention,  and  this  is,  perhaps,  evidenced  by  the  smooth  way  and  unconcerned 
manner  in  which  the  works  foremen  carry  out  the  duty  week  after  week.  The 
modus  operandi,  however,  is  by  no  means  as  simple  as  might  be  supposed,  particularly 
as  far  as  the  maintenance  of  illuminating  power  is  concerned,  also  the  needless 
"  blowing-off  "  and  waste  of  moderately  good  gas.  The  responsibility  is,  of  course, 
increased  owing  to  the  continuity  of  the  process  being  broken,  and  the  consequent 
difficulty  in  ensuring  the  candle-power  being  kept  up  to  statutory  requirements.  In 
the  case  of  the  London  companies,  it  will  be  remembered  that  after  a  good  deal  of 
controversy  the  London  County  Council  proved  their  right  to  the  Sunday  testing  of 
ga's,  some  ten  years  ago.  A  glance  through  the  tables  of  tests  drawn  up  by  the 
Council  from  their  various  stations  shows,  however,  that  the  Sunday  quality  of  the 
gas  compares  very  favourably  with  that  distributed  during  the  week,  and  is  seldom, 
if  ever,  inferior.  In  some  cases  vertical  retort  installations  have  somewhat  modified 
matters,  as  has  also  the  adoption  of  heavy  charges  in  conjunction  with  the  horizontal 
retort.  Needless  to  say,  the  latter  practice  (that  is,  twelve-hour  or  ten-hour  charges) 
has  greatly  facilitated  the  work  of  Sunday  shutting-down. 

REGULATION  OP  THE  CHARGES 

No  hard-and-fast  rules  can  be  laid  down  as  to  the  line  of  action  to  be  followed. 
Much  must  necessarily  depend  upon  the  conditions  and  facilities  prevailing  at  the 
works — such  as  ample  storage  capacity,  the  type  of  retort  settings  to  be  dealt  with, 
and  whether  enrichment  by  carburetted  water  gas  or  other  means  is  available.  The 
most  general  practice  is  to  commence  the  non-gasmaking  period  at  6  a.m.  and  to 
continue  it  until  6  p.m.,  but  in  some  instances,  under  favourable  circumstances,  a 
restart  need  not  be  made  until  10  p.m. 

It  is  proposed  to  describe  here  a  method  which  will  be  found  satisfactory  from 
every  point  of  view,  and  which  has  the  primary  advantage  of  being  extremely  simple. 
Though  the  method  may  be  applied  in  all  cases  (whatever  duration  the  stopping 
period  may  be)  it  will  be  assumed,  for  the  sake  of  simplifying  the  illustration,  that 
no  retort-house  work  is  desired  between  the  hours  of  6  a.m.  and  6  p.m. 

In  this  case  the  last  row  of  retorts  is  charged  so  as  to  be  completed  by  6  a.m.  ; 
thus  for  some  time  the  normal  volume  of  gas  is  coming  away.  As  this  gradually 
decreases,  however,  no  little  precaution  is  necessary  in  the  regulation  of  the  exhauster 


90 


MODERN   GASWORKS   PRACTICE 


and  retort-house  governor.  The  method  of  operating  these  will  be  best  followed  by 
referring  to  the  two  charts  shown  in  Figs.  52  and  53.  In  fact,  the  whole  idea  can 
readily  be  grasped  by  keeping  these  diagrams  in  mind.  Fig.  52  is  a  vacuum  chart 
showing  the  "  pull "  exerted  by  the  exhauster  throughout  the  twenty- four  hours, 
whilst  in  Fig.  53  is  shown  the  vacuum  on  the  hydraulic  main  for  the  corresponding 
period. 

REGULATING  THE  "  DRAW  " 

For  the  first  hour  and  half,  i.e.,  until  7.30,  the  quantity  of  gas  driven  off  will 
permit  the  use  of  the  full  average  "  draw."  Following  this  period  the  volume  of 
gas  gradually  becomes  smaller  and  smaller,  and  the  "  draw  "  at  the  exhauster  is 

reduced  by  degrees,  until 
it  is  no  more  than  half 
an  inch  about  three  hours 
after  the  retorts  were 
charged,  i.e.,  about  9 
a.m.  Meanwhile,  as  will 
be  seen  from  the  second 
chart,  the  retort- house 
governor  is  adjusted  so 
as  to  give  "  level  gauge  " 
on  the  hydraulic  main ; 
this  continuing  until  6 
p.m.  in  the  evening,  when 
the  retorts  are  charged- 
up  once  more.  Similarly, 
the  half -inch  "  draw  "  is 
maintained  at  the  ex- 
hausters until  shortly 
after  6  p.m.,  when  it  is 
raised  gradually  to  the 
usual  amount.  When 
the  exhauster  is  working 
at  such  a  low  vacuum  as 
half  an  inch  it  must  necessarily  be  running  at  its  lowest  possible  speed,  thus  the 
"  pull  "  is  likely  to  be  far  from  steady.  In  order  to  obviate  this,  and  to  put  the 
engine  under  a  greater  load,  it  is  advisable  to  slightly  open  the  by-pass  between  the 
inlet  and  outlet  pipes,  this  having  the  desired  steadying  effect. 

The  advantage  of  working  in  this  manner,  as  will  be  seen,  is  that  there  is  no 
actual  cessation  of  gasmaking,  and  the  exhauster  is  at  work  during  the  whole  twenty- 
four  hours.  In  order  that  this  may  be  the  case,  however,  it  is  essential  that  heavy 
charges  should  be  worked.  If  the  old-fashioned  light  charges  are  in  vogue,  then 
gasmaking  must  inevitably  cease,  and  a  portion  of  the  poor  gas  must  be  blown  away  as 
described  below.  With  the  heavy  charges,  the  make  of  gas  will,  of  course,  diminish 


FIG.  52. — CHAKT  SHOWING  REGULATION  OF  VACUUM  AT  INLET 
or  EXHAUSTER. 


CONTROL   OF  HORIZONTAL  RETORT   SETTINGS        91 


by  degrees,  until,  during  the  final  hour  before  recharging,  it  will  have  dropped  to 
about  7  to  10  per  cent,  of  the  normal  figure. 

GETTING  KID  OF  INFERIOR  GAS 

After  the  final  charge  of  coal  has  been  put  in,  it  is  the  illuminating  power  of  the 
gas  evolved  which  really  decides  the  manner  in  which  the  "  draw  "  is  to  be  regulated. 

O  v  9 

It  is  a  distinct  advantage  to  have  a  special  jet  photometer  run  back  from  the  outlet 
of  the  exhauster  to  the  retort  house,  so  that  the  foreman  in  charge  has  some  indica- 
tion of  the  quality  of  the  gas  soon  after  it  has  been  generated.     When  the  candle- 
power  is  noticed  to  be  dropping,  then  the  "  draw  "  on  the  hydraulic  main  must  be 
regulated  accordingly.     Unfortunately,  in  some  cases,  when  an  inferior  coal  is  being 
used,    the    candle-power 
drops  to  such  an  extent 
that  it  is  no    longer  ad- 
visable to  send  the  gas 
forward  to  the    holders. 
When    this    occurs,     the 
continuity    of   the  work 
has  to  be  broken,    and 
the  exhauster  is  stopped 
while    the    poor    gas    is 
blown     away.      This     is 
best    done    as     follows : 
The  main  valve    at   the 
ouljet  of  the  condensers 
is  closed  and  the  exhaus- 
ter driver  (who  is  stand- 
ing by  waiting  the  signal) 
notices  the  movement  of 
his  chart.    He  then  shuts 
off    the    steam    on    the 
exhauster     engine,     and 
immediately     afterwards 
closes  the  by-pass,  which 
was  opened  when  the  "  draw  "  was  originally  reduced.     Gas  is  still  being  evolved 
from  the  coal  in  the  retorts,  and  an  outlet  must,  of  course,  be  provided  for  this,  or 
some  considerable  pressure  will  be  thrown  upon  the  apparatus  between  the  retorts 
and  the  condensers.     This  should  preferably  be  arranged  for  by  fitting  a  4-inch  pipe 
to  the  inlet  of  the  condensers,  the  pipe  dipping  into  a  seal  pot,  and  being  sealed  in 
liquor  to  a  depth  of  about  half  an  inch.     The  gas  will  at  first  bubble  through  the 
seal  fairly  freely  ;  but  as  the  quantity  evolved  gradually  becomes  less  and  less,  pre- 
caution is  necessary,  for  after  a  time  no  gas  whatever  will  be  evolved,  and  that 
already  in  the  apparatus  will  cool  and  give  rise  to  a  vacuum.      In  consequence,  air  is 
liable  to  be  sucked  in  through  the  blow-off  seal.    In  order  to  prevent  the  possibility 


FIG.  53. — CHART  SHOWINU  REGULATION  OF  VACUUM  BY  RETORT- 
HOUSE  GOVERNOR. 


92  MODERN   GASWORKS   PRACTICE 

of  this  occurring,  the  seal  on  the  blow-off  pipe  is  deepened  until  a  pressure  of  about 
1  inch  is  thrown  upon  the  apparatus. 

THE  PREVENTION  OP  A  VACUUM 

As  serious  results  might  follow  any  intake  of  air  and  the  probable  formation 
of  an  explosive  mixture  in  the  apparatus,  it  will  be  realized  that  the  prevention  of  this 
vacuum  is  one  of  the  outstanding  points  requiring  special  attention  when  temporary 
stops  are  made.  Some  engineers  prefer  the  method  of  slacking-up  the  levers  of  the 
retort  doors,  so  as  to  allow  the  surplus  gas  to  find  an  outlet  in  this  way.  In  the 
method  described  above,  the  lids  are  kept  tightly  sealed  until  the  retorts  are  re- 
charged, and  any  gas  which  is  expelled  goes  out  into  the  open  air  and  not  directly 
into  the  retort  house  itself. 

The  late  Mr.  J.  Tysoe  drew  particular  attention  to  the  liability  of  danger  from 
the  formation  of  this  vacuum,  and  it  is  as  well  to  recall  his  methods  by  quoting  his 
remarks,  which  were  as  follows  :  "It  frequently  happens  that  sufficient  gas  is 
•continuously  driven  off  after  the  exhauster  is  stopped  to  maintain  a  slight  pressure  up 
to  starting-time  in  the  evening ;  but  should  the  pressure  entirely  disappear  before 
that  time,  sufficient  gas  may  be  admitted  to  restore  it  by  means  of  a  2-inch  by-pass 
at  the  inlet  valve  to  the  washers.  On  restarting  the  work,  all  that  is  necessary  is, 
after  a  few  retorts  have  been  charged,  to  open  the  washer  valve  and  close  the  safety 
.seal  at  the  condensers.  By  this  method,  all  risk  of  explosion  in  hydraulic  mains,  of 
which  many  of  us  have  probably  had  experience,  is  entirely  obviated,  perfect  safety 
is  secured,  and  very  little  good  gas  is  lost." 

It  is  interesting  to  note  that  previous  to  the  above  remarks,  Mr.  Tysoe  had 
.said  that  "  Sunday  stoppage  means  a  loss,  however  it  is  carried  out "  ;  which  reminds 
one  of  the  fact  that  at  this  time  (ten  years  ago)  heavy  charges  had  not  been  thought 
of.  Now,  of  course,  given  a  good  coal,  there  is  not  the  least  necessity  for  any  loss 
•whatever. 

CONTROLLING  THE  HEATS 

As  retort  charging  is  discontinued  during  the  stopping  period,  it  is  quite  unneces- 
sary to  keep  the  furnaces  up  to  their  full  working  pitch.  The  last  charges  put  into 
each  retort  are  allowed  to  "  stew  "  during  the  whole  twelve  or  eighteen  hours,  hence 
a,  considerable  amount  of  heat  may  be  dispensed  with  and  fuel  economized.  Ideas 
differ  somewhat  considerably  as  to  the  most  effective  way  of  carrying  this  out,  but 
the  best  and  most  economical  results  are,  no  'doubt,  obtained  by  merely  using 
the  main-flue  damper  to  make  the  adjustment  (this  being  closed  down  to 
.about  75  per  cent,  of  the  normal  amount) ;  whilst,  if  preferred,  the  primary  and 
.secondary  air  slides  may  also  be  closed  down  by  about  half.  The  slides  and  dampers 
may  then  be  opened  again  to  their  full  working  extent  about  3  p.m.,  so  as  to  be  in 
readiness  for  the  fresh  coal  charges  at  6  p.m.  If  the  dampers,  etc.,  are  regulated  in 
this  way  the  furnaces  should  easily  outlast  the  whole  period  without  requiring  further 
-charging  with  fuel.  In  fact,  the  latter  is  one  of  the  features  to  aim  at,  in  order  to 
.do  away  entirely  with  retort-house  labour. 


THE  VALUE  OF  WATER  GAS 

Perhaps  one  of  the  most  serious  objections  to  the  Sunday  stop  is  the  possibility 
of  sudden  demands  arising  from  such  unlooked-for  causes  as  fogs.  However  short 
the  cessation  of  gasmaking  may  have  been,  it  is  always  followed  by  some  inroads  into 
the  gas  available,  and  somewhat  depleted  stocks  are  the  result.  In  some  cases  a 
works  might  conceivably  find  itself  in  an  unenviable  position  should  an  abnormal 
demand  arise  after  the  retort-house  hands  had  been  dismissed  for  the  day.  It  is 
under  such  circumstances  that  the  value  of  a  water-gas  plant  is  felt ;  and,  further- 
more, should  the  quality  of  the  coal  gas  have  suffered  owing  to  that  evolved  during 
the  stop,  a  little  further  carburation  will  soon  put  matters  right.  Here  the  question 
of  diffusion,  and  the  value  of  the  holders  in  this  respect,  plays  some  part.  It  may 
generally  be  taken  for  granted  that  should  any  inferior  gas  go  forward  to  the  holder, 
it  will  thoroughly  intermix  with  better  quality  gas  therein,  with  the  result  that  the 
average  quality  is  quite  up  to  the  normal.  At  times,  however,  there  would  appear 
to  be  some  doubt  as  to  whether  complete  diffusion  does  actually  take  place,  and  in 
holders  in  which  the  inlet  and  outlet  pipe  are  side  by  side  it  seems  possible  that  the 
gas  (or  certainly  some  portion  of  it)  travels  direct  from  one  pipe  to  the  other  without 
any  admixture  with  that  already  in  the  holder.  The  remedy  for  this  is,  of  course, 
to  avoid  working  both  in  and  out  of  the  same  holder. 

FUEL  ECONOMY 

It  is  merely  necessary  to  turn  to  the  prevailing  figures  of  a  decade  or  so 
ago  to  realize  that  fuel  waste  has  been  curtailed  to  an  even  more  striking  extent 
than  the  make  of  gas  per  ton  has  been  augmented,  so  that,  instead  of  having  for 
disposal  only  about  55  per  cent,  of  the  coke  made,  to-day,  with  the  modern  type  of 
producer,  it  is  possible,  with  careful  working,  to  put  on  to  the  market  (including  sales 
to  other  departments  of  the  works)  no  less  than  85  per  cent.  The  true  facts  of  the 
case  are,  perhaps,  better  exemplified  by  comparing  the  heat  units  expended  with  those 
obtained  for  such  an  outlay  in  the  form  of  gas ;  for  whereas  about  80,000  B.Th.U. 
used  to  be  necessary  to  yield  6,000,000  B.Th.U.,  we  now  require  something  less  than 
26,000  B.Th.U.  to  give  a  yield  of  over  7,000,000  B.Th.U.  in  the  gaseous  state.  That 
is  to  say,  a  reduction  of  66  per  cent,  in  the  B.Th.U.  required  has  been  accompanied 
by  a  rise  of  about  17  per  cent,  in  the  B.Th.U.  obtained  in  the  gas.  Even  now  it 
must  be  remembered  that  the  apparently  effective  furnaces  of  the  present  day 
have  by  no  means  approached  perfection,  and  the  amount  of  the  total  heat  utilized 
is  a  notably  small  percentage  of  that  contained  in  the  original  fuel.  For  the  most 
efficient  furnaces  the  loss  in  heat  still  amounts  to  about  45  per  cent,  of  the  total 
contained  in  the  fuel.  This  figure  was  in  the  neighbourhood  of  65  per  cent,  before 
the  introduction  of  regeneration. 

HEAT    BALANCES 

The  question  of  the  heat  balance  of  a  retort  setting  receives  but  meagre  atten- 
tion on  the  ordinary  gasworks.  Results  can  never  be  considered  more  than  very 


94  MODERN   GASWORKS   PRACTICE 

approximate,  owing  to  the  difficulties  with  which  the  investigator  is  faced  and  the 
assumptions  necessary  ;  hence  the  practical  gas  engineer  finds  no  real  use  for  them. 

Of  the  total  heat  due  to  the  combustion  of  fuel  in  non- regenerative  retort  settings 
the  greatest  individual  portion  is  accounted  for  by  that  passing  away  with  the  waste 
gases — this  amounting  to  nearly  59  per  cent,  of  the  whole.  By  the  employment  of 
regeneration,  however,  the  loss  from  this  source  has  been  reduced  by  almost  exactly 
one-half.  The  main  sources  of  thermal  losses  in  a  setting  may  be  briefly  summarized 
as  follows : — 

(a)  Carried  away  in  waste  gases. 

(6)  Carbonization  of  coal,  and  carried  away  by  evolved  gases  and  vapours. 

(c)  Radiation  and  convection  from  brickwork. 

(d)  Lost  in  ashes,  clinker,  etc. 

(e)  Decomposition  of  water  in  fuel  and  moisture  in  inflowing  air.     Also  vaporiza- 
tion of  water  in  ashpan  and  on  firebars. 

(/)  Reduction  of  C02  to  CO  in  producer. 

The  late  Vivian  B.  Lewes  has  shown  that  if  all  the  available  heat  of  the  fuel 
could  be  turned  to  useful  account  only  8-6  per  cent,  of  the  total  weight  of  coke  made 
would  be  required  for  carbonization.  Among  heat-balance  investigators  Euchene 
has  given  figures  which  may  be  taken  as  best  exemplifying  the  manner  in  which  the 
heat  is  expended.  For  the  ordinary  setting  in  which  regeneration  is  not  carried  out 
the  following  results  are  given : — 

NON-REGENERATIVE  SETTING; 
Heat  supplied — 

From  coke         ..'-       .         .         .         ..        .  .         :         .'         ."       .  '     83-6  per  cent. 

From  volatile  products       .          .          .         .  .   '  •   ,          .          .         .         16-4         „ 

.,  100-0  per  cent. 

Heat  expended — 

Per  cent. 

/Carried  up  chimney  as  gases,  34-7  per  cent.                  ]  A.I.<> 
\ A  7          J  Carried  up  chimney  as  water  vapour,  12-5  per  cent,  j 

)  Lost  by  radiation  and  convection   .          .          .          .  .  .       .         .  12-8 

^Lost  in  ash  and  clinker.          .  "''..'.   '      «          •          •  •  ''••'••         •  0-7 

In  retorts     [Used  in  distillation  of  coal      .          .       \          .          .                   .          .  15-7 

39-3         ^.Escaping  by  ascension  pipe,  in  volatile  constituents  ...         .  10-4 

per  cent.      ^Escaping  in  hot  coke      .         ..        t.          .          .'        .  ...  13-2 

100-0 


The  chief  point  to  be  noticed  is  that  in  this  type  of  setting  only  16  per  cent,  of 
the  total  heat  supplied  actually  goes  to  fulfil  the  primary  function  of  the  setting— i.e., 
the  distillation  and  decomposition  of  the  coal  and  its  primary  products. 

REGENERATIVE  SETTING. 
Heat  supplied — 

From  coke         .         .-..-.          ...          •  •        77-4  per  cent. 

From  volatile  products       .  •  ; .          .  22-6         „ 

100-0  per  cent. 


CONTROL   OF  HORIZONTAL   RETORT   SETTINGS         95 


Heat  .expended — 


In  setting 

45-9 
per  cent. 

In  retorts 

54-1 
per  cent. 


/Carried  up  chimney  as  gases,  19-9  per  cant.  \ 

Carried  up  chimney  as  water  vapour,  5-3  per  cent.    J 
"1  Lost  by  radiation  and  convection   .          .  . 

VLost  in  ash  and  clinker .          .          .          .          .          .         •» 

I  Used  in  distillation  of  coal     .  |  . 

i  Escaping  by  ascension  pipe,  etc.,  in  volatile  constituents 

(Escaping  in  hot  coke      .          .         .          .          ... 


Per  cent. 
.      25-2 

.      19-9 
0-8 

.      21-4 

.      13-8 

18-9 


100-0 

The  experiments  of  D.  D.  Barnum,  of  Worcester,  Mass.,  in  general  corroborate 
the  above  figures,  except  in  one  important  respect.  Barnum  obtained  his  figures 
for  a  bench  in  which  regeneration  was  carried  out  entirely  at  the  expense  of  the 
producer.  The  total  loss  accounted  for  by  the  chimney  amounted  to  47-6  per  cent., 
and  that  utilized  for  distillation  and  decomposition  to  21-6  per  cent. 

A  comparison  between  Euchene's  figures  and  those  of  Barnum  is  given  below. 
'The  former  are  converted  from  K.C.U.  per  100  kilogrammes  to  B.Th.U.  per 
100  lb..  so  that  both  sets  are  expressed  in  similar  units. 

REGENERATIVE  SETTINGS. 


EUCHENE. 


BARNUM. 


B.Th.U.  per  100  lb. 


Heat  contained  in  fuel 


"Heat  lost — 

In  ashes 

In  flues 

In  volatile  matter 

By  radiation    .      , 
Heat  in  coke 


180,547 


2,131 

58,768 
32,398 
45,550 
44,253 


Total  heat  expended    . 
Absorbed  during  distillation 
Dispersed  during  distillation 


183,100 
2,553 


215,623 


122,377 
23,333 
20,931 
33,708 


200,349 
15,274 


The  chief  point  to  be  noticed  is  that  whereas  Euchene  finds  heat  to  be  liberated, 
Barnum's  results  indicate  an  absorption  due  to  distillation.  Undoubtedly 
looih  exothermic  and  endothermic  reactions  occur  simultaneously  during 
•carbonization,  and  whilst  more  recent  authorities  agree  as  to  the  ultimate 
•endothermicity  of  the  process,  its  actual  nature  is  still  open  to  question.  The  most 
recent  research  in  this  direction  has  been  carried  out  by  Cobb  and  Rollings,  who 
"Conclude  that  the  exothermic  reactions  commence  at  1,130°  Fahr.  and  continue  until 


96  MODERN   GASWORKS   PRACTICE 

some  high  temperature  is  reached;  but  at  1,380°  Fahr.  endothermic  reactions 
commence  which  mask  the  exothermic  effect  above  that  temperature.  Moreover, 
whilst  prolonged  heating  at  1,380°  Fahr.  does  not  effect  a  completion  of  the  exother- 
mic reactions,  it  would  appear  that  it  does  complete  the  endothermic  reactions, 
since  after  heating  at  1,380°  Fahr.  there  is  some  evidence  of  exothermic  reactions 
up  to  1,650°  Fahr. 

In  the  item  "  total  heat  supplied  "  in  Euchene's  figures  it  should  be  mentioned 
that  the  percentage  attributed  to  "  volatile  products  "  indicates  the  quantity  of 
heat  evolved  in  the  retort  owing  to  the  supposed  nature  of  the  reactions  ;  that  is,  it 
is  the  heat  of  the  formation  of  the  original  coal,  which  is  liberated  by  the  process  of 
carbonization.  Mahler  in  his  researches  observed  a  loss  of  3  J  per  cent,  of  the  original 
heat  units  in  coal  due  to  carbonization,  which  he  looked  upon  as  representative  of 
the  heat  liberated  by  the  process.  This  figure,  however,  takes  no  account  of  "  scurf  " 
deposited  in  the  retorts,  or  of  naphthalene,  for  both  of  which  some  reduction  must 
be  made. 

Further  investigations  have  been  conducted  by  H.  Poole,  who  finds  a  balance, 
due  to  liberated  heat,  of  3-05  per  cent. 

Poole's  balance  of  heat  units  is  as  follows  : — 

In  original  coal  before  distillation,   13,260  B.Th.U.  per  Ib. 
After  distillation,  B.Th.U.  recovered — 

In  coke       .'...  ,  .          .          .''":.  .  8,296  B.Th.U. 

In  tar          ...  .  ...          .          .          .  .        614         „ 

In  gas       "\         .    "  ..,  '-,,..  ..        ','•••  •  3,418 

Lost  in  water,  etc.  527         ,, 


12,855  B.Th.U. 
Unaccounted  for.      •    ..'•       ..,"..       .          .          .        405         „         or  3-05  per  cent. 


13,260  B.Th.U. 

THE   CURTAILMENT   OF  LOSSES 

The  economical  operation  of  the  modern  regenerator  depends,  perhaps,  more 
upon  its  structural  features  than  upon  any  refinements  in  its  working  which  may 
subsequently  be  introduced  ;  for,  more  often  than  not,  a  producer  is  designed  with 
but  little  thought  to  the  many  small  yet  telling  items  that  count,  with  the  result 
that,  however  much  attention  it  may  afterwards  receive,  it  is  never  possible  to 
economize  beyond  a  moderate  extent.  The  main  point  to  be  kept  in  view  is  the 
most  effectual  means  for  abstracting  the  maximum  quantity  of  heat  from  the  fuel — 
that  is,  the  greatest  possible  proportion  of  its  calorific  value — and  the  utilization 
of  this  heat  with  the  minimum  of  loss.  On  gasworks  nowadays  the  fuels  used,  almost 
without  exception,  are  coke  and  breeze  ;  although  with  the  price  of  coal  slack  at  3s.  or 
so  per  ton  lower  than  that  of  coke,  the  Mond  producer  may  be  a  familiar  feature  of 
the  large  gasworks  of  the  future.  Tar  as  an  agent  for  retort  or  boiler  heating  may  be 
dismissed  from  serious  notice,  as  the  high  price  it  is  now  commanding  has  rendered 
its  use  unprofitable,  although  it  became  quite  popular  as  a  fuel  some  years  ago. 


CONTROL   OF   HORIZONTAL   RETORT   SETTINGS       '97 

The  price  at  that  time,  however,  was  Id.  (or  less)  per  gallon  ;  now  it  is  nearly  three 
times  as  much,  and  tar  cannot  compete  with  coke  when  costing  more  than  \\d.  per 
gallon. 

ITEMS   FOR   CONSIDERATION 

Owing  to  the  different  methods  of  firing  now  employed  on  gasworks,  that  is, 
whether  individual  or  "  outside  "  producers,  generators  or  regenerators,  it  is  difficult 
to  lay  down  hard-and-fast  rules  of  construction  and  working  applicable  to  all  systems  ; 
but  the  principal  heat  losses  liable  to  affect  all  types  of  producers  may  be  summar- 
ized as  follows  : — 

1.  Incomplete  combustion  of  carbon  to  CO. 

2.  Incomplete  combustion  of  CO  to  C02. 

3.  Too  rapid  travel  of  primary  air  through  fuel  bed. 

4.  Too  rapid  travel  of  hot  gases  through  setting,  or  too  much  chimney  draught. 

5.  Losses  due  to  fuel  falling  through  firebars  into  ashpit  or  removed  with  clinker. 

6.  Radiation  and  convection  losses. 

7.  Extensive  variation  in  composition  of  producer  gas. 

8.  Insufficiency  of  gas. 

With  regard  to  the  first  two  items,  these  are,  of  course,  avoidable,  providing 
that  no  faults  have  been  introduced  in  the  design  of  the  producer ;  and  they  are 
best  remedied  by  systematic  analysis  of  both  the  producer  and  waste  gases.  It  is 
necessary,  however,  to  emphasize  the  fact  that  satisfactory  gas  tests  do  not  in  any 
sense  ensure  good  heats  ;  for,  although  the  combustibles  may  be  present  in  ideal 
proportions,  it  is  quite  possible  that  they  may  not  be  present  in  sufficient  quantities. 

The  third  item  in  the  list  lends  itself  to  adjustment,  providing,  again,  that 
the  construction  of  the  producer  is  not  to  blame.  If  this  is  the  case  the  trouble  can 
usually  be  traced  to  an  insufficiency  of  grate  area,  the  importance  of  providing 
adequately  for  this  having  been  somewhat  underestimated  by  designers  in  the  past. 
Slow  travel  of  the  primary  air  through  the  fuel  bed  is  ensured  with  abundant  grate 
area  (see  Chapter  III,  p.  63)  ;  whilst  there  will  be  less  "  slip  "  up  the  sides  of  the 
furnace,  and  a  shallower  bed  of  clinker  will  be  formed.  Owing  to  the  extended 
contact  of  primary  air  and  coke,  the  quality  of  the  gas  will  be  materially  improved. 

On  no  account  should  the  velocity  of  draught  be  so  great  as  to  draw  off  the  gases 
from  the  setting  before  they  have  been  cooled  down  in  the  regenerators  by  at  least 
700°  Fahr.,  and  the  base  of  the  waste-gas  channel  should  be  almost  devoid  of  colour. 
This  question  of  draught  may  affect  the  formation  of  the  producer  gas  in  two  ways. 
First,  the  rate  of  travel  of  air  through  the  fuel  bed  may  be  sufficiently  slow  for  the 
formation  of  carbon  dioxide  in  the  lower  portions  of  the  furnace,  but  the  time  of 
contact  may  not  be  sufficiently  long  for  the  reduction  of  this  gas  to  carbonic  oxide — 
hence  an  excessive  proportion  of  incombustibles  in  the  furnace  gas  may  result.  So 
far  as  the  draught  is  concerned  it  is  the  chimney  height  and  flue  area  which  are 
of  importance  in  this  respect  (see  p.  64). 

H 


98  MODERN   GASWORKS   PRACTICE 

CLINKER  AND   ASH 

A  word  is  necessary  here  with  regard  to  the  troublesome  formation  of  clinker 


some  types  of  furnace.  When  clinker  difficulties  set  in,  it  is,  perhaps,  the  natural 
inclination  of  the  man  charged  with  its  removal  to  make  disparaging  reference  to  the 
•coke  supplied  to  the  furnaces  at  the  time.  A  coal  with  a  heavy  ash  content  must 
mecessarily  increase  the  amount  of  inert  matter  to  be  cleaned  from  the  furnace  ; 
t»ut  tne  secret  of  long  periods  without  clinkering  known  to  users  of  vertical  retorts  is 
.<due  to  the  nature  of  the  non-  combustible  portions  of  the  fuel  after  passing  through  the 
tfurnace.  With  a  strong  draught  a  large  proportion  of  the  ash  in  the  fuel  is  fluxed, 
with  the  consequent  formation  of  clinker  ;  whilst  with  a  slow  draught  the  heat 
•of  the  furnace  is  reduced,  with  the  result  that  little  fluxing  takes  place,  and  ash 
instead  of  clinker  is  the  outcome.  Clinker  prevents  the  admission  of  air,  so 
that  local  combustion  in  the  fuel  bed  takes  place.  With  ash,  on  the  other  hand, 
iurnace  cleaning  is  a  small  matter  ;  and  it  is  possible  to  find  works  in  which  clinker- 
ing  of  the  fires  is  practically  unknown.  With  the  Munich  chamber  system  of  car- 
bonization the  operation  is  carried  out  once  in  three  months,  although  "  pricking- 
np  "  is  resorted  to  once  a  day.  The  remedy  for  the  excessive  formation  of  clinker 
is  simple,  and  can  be  directly  traced  to  the  introduction  of  large  grate  areas  and  slow 
travel  of  gas  ;  also  in  some  cases  to  the  employment  of  special  water-cooled  grates. 

MAXIMUM   COMBUSTION   TEMPERATURE 

The  evil  of  admitting  excessive  quantities  of  air  should  perhaps  receive  some 
mention  here  ;  and  it  must  be  borne  in  mind  that  the  highest  temperature  which  can 
be  obtained  by  the  combustion  of  fuel  is  that  to  which  the  products  are  raised  on  their 
formation  by  the  heat  dispersed.  Thus,  the  larger  the  volume  of  gas  to  be  heated 
the  less  will  the  temperature  be.  It  is  in  this  respect  that  regeneration  tells  ;  for 
when  the  air  is  heated  before  combustion  is  allowed  to  take  place,  the  heat  of  the 
air  is  added  to  the  heat  of  combustion.  Thus  the  quantity  of  heat  available  for 
raising  the  temperature  of  the  products  is  very  much  greater. 

With  regard  to  vertical  retort  furnaces  and  the  economical  lines  on  which  they 
are  operated,  it  may  be  pointed  out  that  in  the  Glover-  West  type  the  secondary 
air  is  preheated  by  circulating  around  the  coke  chamber  constituting  the  bottom 
three  feet  of  the  retort,  and  in  this  way  the  sensible  heat  is  extracted  and  turned  to 
useful  account.  In  the  Woodall-Duckham  system  the  coke  is  discharged  more  or 
less  cold,  but  in  recent  installations  a  new  device  has  been  made  use  of  by  means  of 
which  the  primary  air  passes  through  fireclay  tubes  adjacent  to  the  base  of  the  retort, 
thus  utilizing  heat  which  was  originally  lost. 

A  warning  is  necessary  here  with  regard  to  filling  up  furnaces  with  partly  car- 
bonized or  "  tacky  "  coke  ;  that  is,  if  the  charges  in  the  retorts  are  not  burnt  off, 
their  discharging  into  the  furnaces  should  be  postponed.  The  effect  of  such  sticky 
fuel  is  to  restrict  the  primary  air  supply,  by  closing  up  the  interstices  between  the 
particles  of  coke;  and  irregular  combustion  is  the  result.  Furthermore,  a  certain 
amount  of  heat  is  absorbed  in  driving  off  the  volatile  constituents  remaining  in  the 
coke,  although  these  constituents  may  themselves  be  combustible. 


CONTROL   OF  HORIZONTAL   RETORT   SETTINGS        99 

SECONDARY  AIR  DIRECTION 

In  retort  settings  of  nearly  every  design  it  is  customary  to  find  that  the  secondary  - 
air  channels  are  arranged  round  the  furnace  arch  in  such  a  manner  that  when  the 
heated  air  emerges  it  meets  the  gases  from  the  producer  practically  at  right  angles. 
Until  recently  the  advisability  of  this  method  has  never  been  questioned,  but  opinions 
now  appear  to  be  undergoing  some  change.  Dr.  Karl  Bunte,  in  a  recent  paper  read 
before  the  German  Association  at  Strassburg,  pointed  out  the  shortcomings  of  this 
procedure,  and  stated  that  in  all  the  more  perfect  of  modern  settings  such  conditions 
are  obviated.  The  effect  of  introducing  the  secondary  air  in  a  strong  current  at  right 
angles  to  the  producer  gases  is  to  give  rise  to  too  thorough  intermixing  of  the  air  and 
gases,  with  the  result  that  short  flames  are  produced.  In  order  to  ensure  as  uniform 
heating  throughout  the  setting  as  possible  such  short  flames  should  be  avoided. 
To  this  end  the  gas  and  air  streams  should  meet  on  almost  parallel  courses,  in  which 
case  admixture  of  the  two  is  gradual,  and  flames  of  larger  volume  are  produced. 
The  majority  of  existing  settings  can  be  readily  adapted  to  meet  this  requirement. 
The  method  of  dealing  with  a  typical  case  is  shown  in  Fig.  42.  In  this  instance 
the  secondary  air  is  conducted  in  the  ordinary  way  to  the  apex  of  the  furnace  arch 
by  means  of  horseshoe  channel  blocks.  As  generally  laid,  the  blocks  provide  for 
admixture  taking  place  very  nearly  at  right  angles.  A  simple  and  effective  means  of 
providing  for  a  more  parallel  flow  is  to  split  a  9-inch  firebrick  diagonally,  and  to 
insert  it  under  the  final  blocks  each  side  as  shown,  so  that  the  latter  are  given  an 
upward  cant.  The  method  will  be  clearly  followed  from  the  sketch. 

It  is  interesting  to  recall  here  that  the  flame  development  takes  place  quite 
differently  in  vertical  retort  firing.  In  this  case  the  flame  follows  a  spiral  course 
from  below  upwards  (in  the  Glover- West  and  Dessau  systems),  or  from  above  down- 
wards (in  the  Woodall-Duckham  system).  The  latter  arrangement  provides  for 
the  heating  of  the  upper  third  of  the  retort  by  eight  burners,  whereas  the  lower 
portions  of  the  charge  are  situated  in  a  comparatively  cool  zone.  In  the  Dessau 
furnace  the  regulation  of  the  flame  development  is  extremely  well  effected  by  means 
of  brattices  which  ensure  the  gas  streams  taking  parallel  courses,  whilst  at  suitable 
intervals  mixing  blocks  are  inserted  which  thoroughly  churn  up  the  inflowing  air  and 


CHAPTER   V 
VERTICAL   RETORTS   AND   CHAMBER   OVENS 

THE  present-day  popularity  of  the  vertical  retort  and  chamber  oven  is,  no  doubt,  the 
natural  outcome  of  the  growing  preference  for  carbonization  in  bulk,  and  the  tendency 
for  the  gas  engineer  to  relieve  himself  as  far  as  possible  of  the  vagaries  of  manual 
labour.  Although  the  evolution  of  the  vertical  retort  in  its  modern  form  has  taken 
place  within  the  last  decade,  the  idea  is  by  no  means  a  new  one,  for  so  long  ago  as 
1828  Brunton  patented  an  intermittent  system  having  many  features  similar  to 
those  of  the  prevailing  types  of  to-day. 

The  systems  of  vertical  retorts  at  present  in  use  may  be  divided  into  three 
distinct  types. 

(a)  Continuous  types. 

(6)  Intermittent  types. 

(c)  Continuous- intermittent  types. 

Of  these,  the  first-named  system  aims  at  solving  the  problem  of  ideal  carboniza- 
tion ;  that  is,  the  continuous  admission  of  relatively  small  charges  of  coal  accom- 
panied by  the  continuous  extraction  of  that  which  has  undergone  distillation.  Hence, 
undesirable  variations  in  the  quantity  of  gas  evolved  (inseparable  from  intermittent 
charging)  are  completely  avoided.  Intermittent  types  of  vertical  retorts  embrace 
the  principles  employed  in  the  horizontal  bench,  i.e.  a  definite  charge  of  coal  is 
arranged  for  at  stated  periods,  the  retort  being  emptied  at  the  end  of  the  distillation 
spell.  Continuously  operated  retorts  are  never  empty.  Continuous-intermittent 
systems  are  those  whose  design  permits  of  the  retorts  being  operated  on  either  the 
continuous  or  intermittent  plan.  So  far  they  have  not  gained  much  headway  in  this 
country ;  but  as  they  are  of  most  recent  origin,  their  wide  adoption  is  scarcely 
to  be  looked  for  at  present. 

It  is  not  proposed  to  discuss  here  forms  of  .vertical  retorts  other  than  those 
which  have  been  actually  employed  in  this  country  and  are  at  work  at  the  present 
time.  In  addition  to  the  systems  enumerated  below  many  others,  originating  from 
America  and  the  Continent,  are  to  be  found.  The  systems  in  operation  in  the 
United  Kingdom  are  : — 

(a)  Woodall-Duckham       .         .         .         .     Continuous. 

(&)  Glover- West        .  .        ..         .     Continuous. 

(c)  Dessau       .         .         .         .  .     Intermittent. 

(d)  Elland  system    .         .         .  .     Continuous  or  intermittent. 

100 


VERTICAL   RETORTS   AND   CHAMBER  OVENS       101 

(e)  Glasgow  sytem    .....     Continuous- intermittent. 

(/)  Herring's  system  ....     Continuous. 

(g)  Holmes- Winstanley      ....     Continuous  or  intermittent. 

Among  the  earlier  systems  was  the  Settle-Padfield,  in  which  the  retort  com- 
menced in  a  vertical  plane,  but  turned  off  at  an  angle  at  the  base,  so  that  the  coke 
was  discharged  through  the  side  of  the  bench,  and  not  at  the  bottom.  Charging 
was  arranged  for  on  continuous  lines,  but  the  coke  was  withdrawn  at  definite 
intervals,  so  that  the  amount  of  free  space  in  the  retorts  was  subject  to 
variation.  The  system  has  now  been  discarded. 

It  is  difficult  to  draw  comparisons  between  the  continuous  and  intermittent 
systems.  In  most  cases  the  engineer  must  take  into  consideration  the  prevailing 
conditions,  and  select  his  system  accordingly.  In  comparison  with  horizontal 
systems  the  following  advantages  may  be  claimed  for  vertical  retorts. 

(1)  Greater  yield  of  gas  on  a  given  area.     For  horizontals  the  average  yield 
is  200  to  250  cubic  feet  per  square  foot  of  ground  area.     For  verticals  this  figure 
may  be  increased  to  as  much  as  475  feet  per  square  foot  of  area — according  to  the 
system. 

(2)  Better  conditions  in  retort  house  and  no  very  arduous    labour.     Less 
clinkering. 

(3)  Low  consumption   of  fuel  (see  p.  47).       This   claim,   although  invariably 
made  for  vertical  systems  of  the  continuous  type,  must  be  viewed  with  a  certain 
amount  of  reserve.     Such  figures  as  have  been  given  usually  favour  the  vertical 
systems,  but  these  are  mostly  the  outcome  of  trial  runs,   and  are  not  altogether 
borne  out  by  extended  practical  working. 

(4)  Control  of  heats  as  regards  various  sections  of  the  retort.     In  the  modern 
horizontal  setting  the  multiple  control  of  secondary  air  ensures  almost  as  perfect 
adjustment. 

(5)  Each  particle  of  coal  is  subjected  to   exactly  similar  treatment.     This 
means  that  all  coal  passes  in  turn  through  the  various  temperature  zones  prevailing 
in  the  retort,  and  there  is  no  trouble  with  uncarbonized  portions  of  coal,  as  is  often 
the  case  near  the  mouthpieces  of  horizontal  settings. 

(6)  With  continuous  systems  the  gas  is  certainly  produced  in  more  uniform 
quality. 

(7)  The  heat  in  the  coke  is  in  most  systems  utilized,  and  not  wasted  as  in 
horizontals. 

(8)  The  gas  is  not  subjected  to  degradation  by  long  contact  in  a  large  free 
space.     This  claim  requires  some  substantiating  when  made  in  comparison  with 
horizontals  working  with  completely  full  charges.     It  must  be  remembered  that  the 
gas  evolved  from  the  lower  portions  of  the  vertical  charge  has  to  travel  to  the  outlet 
pipe  partly  through  red-hot  coke  and  partly  against  the  sides  of  the  retorts  (see  p.  284). 

(9)  Make  per  ton  "  may  in  some  cases  be  increased  by  steaming  the  base  of 
the  charge,  when  the  coal  is  sufficiently  good  to  allow  of  this. 

(10)  Heavy  and  complicated  charging  and  discharging  machinery  is  eliminated 
— thus  wear  and  tear  expenditure  is  reduced. 


102  MODERN   GASWORKS   PRACTICE 

(11)  Labour  costs  per  ton  of  coal  per  diem  are  from  one-half  to  one-third  less 
than  with  horizontal  retorts. 

The  claims  of  the  horizontal  bench  may  be  set  down  as  follows  : — 

(1)  The  coke  in  vertical  retorts  has  occasionally  a  tendency  to  "jam"  up. 
This  particularly  refers  to  the  intermittent  types. 

(2)  The  retorts  are  more  difficult  to  repair  during  operation,  and  as  the  continu- 
ous retort  is  only  cleared  at  long  intervals  a'  leak  may  go  undetected  for  some  time. 

(3)  The  capital  cost  per  ton  of  coal  per  maximum  day  is  in  general  higher  for  the 
vertical  systems.     Inclusive  of  complete  bench  and  foundations,  coal-handling  plant, 
power-operating  plant,  coke-handling  plant,  but  exclusive  of  retort  house,  a  vertical 
installation  (according  to  size)  will  cost  from  about  £150-£200  per  ton  of  coal.     The 
cost  for  a  horizontal  plant  would  be  £110-£140  per  ton,  and  in  isolated  cases  less  than 
the  lower  limit  given. 

(4)  In  continuously  operated  types  any  breakdown  in  machinery  usually  entails 
greater  inconvenience. 

So  far  as  the  relative  jnerits  of  the  two  systems  of  verticals  are  concerned  the 
advocates  of  the  continuous  type  lay  claim  to  the  following  advantages  over  the 
intermittent : — 

(1)  No  air  pulled  in,  because  doors  of  retort  are  always  closed. 

(2)  Quality  of  gas  always  constant. 

(3)  Each  piece  of  coal  undergoes  the  same  treatment. 

As  regards  the  merits  of  the  intermittent  systems  the  following  points  are 
drawn  attention  to  : — 

(1)  There  is  no  machinery  to  breakdown. 

(2)  The  retorts  are  accessible  at  any  time  for  repairs,  etc. 

(3)  Wear  and  tear  is  less,  as  there  are  no  continuously  working  parts. 

(4)  Retorts  are  said  to  last  longer,  as  no  abrasion  takes  place  by  continuous 
movement  of  the  coke. 

(5)  Increased  yield  of  gas  per  ton,  by  steaming. 

THE    WOODALL-DUCKHAM    SYSTEM 

This  system,  which,  with  the  Glover- West,  has  made  more  headway  than  any 
other  type  in  this  country,  has  undergone  considerable  modification  since  its  introduc- 
tion in  1903.  Continuous  charging  and  discharging  was  then  arranged  for ;  the 
base  of  the  retort  was  water-sealed,  and  the  coke,  after  passing  the  extractor,  was 
quenched  in  the  seal  and  removed  by  means  of  a  short  length  of  conveyor.  Fjve 
years  later  the  present  system  of  coke- extraction  was  introduced  and  the  water- 
seal  abolished.  The  amount  of  coal  passing  into  the  retort  and  the  rate  at  which  the 
charge  descends  are  automatically  governed  by  the  speed  of  the  coke  extractor. 
The  coal  occupies  from  seven  to  eight  hours  in  its  passage  through  the  retort, 
which  is  25  feet  in  length  and  of  rectangular  tapered  shape. 

Breadth  and  width  of  retort      .         .         .     Top,  3  feet  10£  inches  by  8  inches. 
Breadth  and  width  of  retort      .         .         .     Bottom,  5  feet  3  inches  by  18£  inches. 


VERTICAL  RETORTS  AND   CHAMBER  OVENS       103 

The  walls  of  the  retorts  are  formed  of  tongued  and  grooved  bricks,  panelled 
out  at  the  back  so  that  heat  is  readily  conducted  from  the  flues  to  the  charge  (Fig.  51). 


FIG.  54. — SECTION  OF  WOODALL-DUCKHAM  VERTICAL  SLOT  RETORT,  SHOWING  METHOD  OF  BONDING- 
SPECIAL  BRICKS. 

A  point  worthy  of  notice  is  that  in  this  system,  in  contrast  to  the  Glover- West,  top- 
heating  of  the  retorts  is  arranged  for,  i.e.  the  producer  gas  is  admitted  at  the  top  of 


FIG.  55. — THE  WOODALL-DUCKHAM  COKE  EXTRACTOR. 

the  vertical  flues  surrounding  the  retorts  and  travels  downwards.     The  device 
employed  for  extracting  the  coke  is  shown  in  Fig.  55.     The  chief  points  to  note  ini 


FIG.  56. — THE  WOODALL-DUCKHAM  CONTINUOUS  RETORT  SYSTEM. 


104 


VERTICAL   RETORTS   AND   CHAMBER  OVENS       105 

its  construction  are  that  it  is  designed  so  that  no  shearing  or  cutting  of  the  coke  takes 
place,  whilst  it  is  relieved  of  the  weight  of  the  charge  in  the  retort  by  curving  the  cast- 
iron  extractor  chamber.  The  speed  of  the  extractor  may  be  varied  to  suit  the 
type  of  coal  undergoing  carbonization,  but  on  an  average  it  is  one  revolution  in  from 
fifty  to  seventy  minutes.  Driving  takes  place  by  means  of  a  reciprocating  bar  con- 
tinuous throughout  the  whole  length  of  the  bench.  In  the  latest  installations  the 
rotary  extractor  has  given  way  to  an  endless  belt  device.  The  coke  after  passing 
the  extractor  drops  into  a  receiving  hopper,  which  is  emptied  about  every  three  hours. 
Quenching  takes  place,  not  by  means  of  water,  but  by  the  circulation  of  the  primary 
air  around  the  base  of  the  retort,  so  that  the  coke  leaves  the  chamber,  and  is  charged 
into  the  producer,  in  a  cold  state. 

The  coal-feeding  device  will  be  readily  understood   by   reference   to   Fig.  56. 
It  consists  of  a  gas-tight  hopper  of  mild  steel  plates  mounted  on  a  special  casting 


TarOutCet  ^ 


FIG.  57. — THE  WOODALL-DUCKHAM  HYDRAULIC  MAIN. 

attached  to  the  retort  mouthpiece.  This  hopper  is  closed  at  the  top  by  a  circular 
gas-tight  valve,  operated  by  hand  about  every  three  hours.  The  fropper  requires 
about  ten  seconds  to  be  filled.  A  special  form  of  indicator  shows  the  rate  of  flow 
of  the  coal  into  the  retort. 

In  this  system  the  gas  is  taken  off  by  a  hydraulic  main  (Fig.  57)  ;  and  a  unique 
feature  is  the  provision  of  a  regulating  division  plate  so  that  the  free  space  through 
which  the  gas  must  pass  before  leaving  the  retort  is  variable  at  will.  The  extent  of 
this  free  space  amounts  to  0-7  to  1-4  per  cent,  of  the  total  volume  of  the  retort. 

The  following  items  are  tabulated  for  reference  : — 

Coal  carbonized  per  retort  per  max.  diem     .  4£  to  5J  tons,  according  to  class  of  coal  in  ust. 

Average  yield  per  retort  per  max.  diem  .      .  60,000  to  70,000  cubic  feet. 

Number  of  retorts  in  each  setting        .      .      .  Four  or  two. 

Grate  area  of  producer 28  square  feet  per  setting  of  four  retorts. 


FIG.  58. — THE  GLOVER-WEST  VERTICAL  RETORT  SYSTEM. 
106 


VERTICAL   RETORTS  AND   CHAMBER  OVENS       107 


Grate  area  per  lineal  foot  of  retort 
Costs. — Complete  bench,  including  foundations, 
coal-handling  plant,  and  coke-handling  plant, 
but  exclusive  of  house 

Complete  bench  only,  inclusive  of  foundations 

Cost  of  house,  with  foundations  (per  ton  of 
coal  per  max.  diem) 

Power  required  per  ton  of  coal  per  max.  diem 

Power  costs  (minimum) — 

Coke  extractor , 

Coke-handling  plant 

Coal-handling  plant 

Average  period  of  clinkering  producer. 


0-28  square  foot. 


£140-£180   per  ton  of    coal  per   max.   diem, 

according  to  size  of  plant. 

£110-£155    per  ton    of    coal    per  max.  diem> 

according  to  size. 

£25-£45,  according  to  size  of  plant. 
1-8  b.h.p. 

%d.  per  ton  of  coal  carbonized,  at  Id.  per 

unit  for  electricity. 


48  hours. 


It  will  be  noticed  that  the  grate  area  of  the  producer  is  considerably  larger  in 
proportion  than  that  of  the  ordinary  horizontal  bench,  this  accounting  for  the  longer 
periods  for  which  the  furnace  will  go  without  clinkering.  At  intervals  of  about 
six  weeks  the  retorts  are  emptied  and  stood  off  for  "  scurfing." 

THE   GLOVER-WEST   SYSTEM 

This  important  system  of 
vertical  retorts  was  the  outcome 
of  patents  taken  out  in  1905  by 
Young  and  Glover,  founded  in 
constructional  details  on  the  Scot- 
tish shale  retorts.  In  1909,  the 
present  Glover  and  West  system 
was  introduced.  As  in  the 
Woodall-Duckham  system,  the 
ideal  of  continuous  carbonization 
is  aimed  at,  but  the  methods  of 
arranging  for  this  vary  to  some 
considerable  extent  in  detail. 
First,  the  retorts  are  oval  in  sec- 
tion instead  of  rectangular,  and 
are  built  up  of  concentric  fireclay 
rings,  whilst  the  bottom  3  feet  of 
each  is  composed  of  cast-iron  or 
special  silica  blocks,  and  forms  a 
regeneration  chamber  for  the 
secondary  air  entering  the  pro- 
ducer. The  passage  of  the  gas 
from  the  retorts  will  be  readily 
understood  from  the  figure,  an  FIG.  59. — COKE  CHAMBERS,  GLOVER-WEST  SYSTEM. 


108  MODERN   GASWORKS   PRACTICE 

outlet  being  provided  at  the  base  of  each  coal- feeding  hopper,  whence  the  gas 
is  conducted  by  a  7-inch  pipe  to  a  dry  main.  Each  outlet  pipe  is  fitted  with  a 
valve  which  is  brought  into  use  when  a  retort  is  out  of  action  for  scurfing 
purposes.  Coke  extraction  is,  of  course,  continuous,  and  governs  the  rate  at 
which  coal  is  delivered.  The  extractor  consists  of  a  slowly  revolving  vertical 
worm,  driven  by  gas  or  electricity  (about  3  h.p.)  at  a  speed  of  one  revolution 
in  about  thirty  to  forty  minutes.  The  extractor  is  made  in  two  halves,  so  that  one 
Jhalf  may  be  removed  and  the  retort  readily  inspected.  A  novel  feature 
enables  the  speed  of  the  individual  extractors  to  be  regulated,  so  that  if  differ- 
ing types  of  coal  are  in  use  in  the  retorts  the  speed  of  each  worm  can  be  adjusted 
to  suit  the  particular  class  of  coal.  Dropping  from  the  extractor  the  coke  passes 
into  a  chamber  fitted  with  a  self-sealing  lid  (Fig.  59),  and  is  removed  from  this 
at  intervals  of  about  two  hours.  The  system  of  heating  the  retorts  differs  from 
that  of  Woodall  and  Duckham  in  that  combustion  takes  place  towards  the  bottom 
of  the  retorts  and  the  waste  gases  pass  around  the  upper  portions  into  horizontal 
circulating  chambers  before  finding  their  way  to  the  chimney.  On  account  of  the 
•cooling  action  of  the  secondary  air  passing  around  the  base  of  the  retort,  no  water- 
•quenching  is  necessary,  and  the  coke  is  discharged  from  the  lower  chambers  prac- 
tically cold.  The  producers  are  charged  up  with  this  cold  coke  at  intervals  of  about 
four  hours.  The  more  important  details  of  the  system  are  summarized  below : — 

Shape  of  retorts Oval. 

Length  of  retorts .  •  •"•      •      19  feet  to  25  feet. 

Breadth  and  width v  .      .      •     At  top,  from  27  inches  to  33  inches  by  from 

12  inches     to     8  inches ;    at     base,     from 

36  inches  to  39  inches  by  from  21  inches  to 

18  inches. 

Number  of  retorts  in  each  bed.  .  .  .  .  ^jsually  eight. 
•Coal  carbonized  per  retort  per  max.  diem  .  2j  to  3£  tons. 
Average  yield  per  retort  per  max.  diem  .  .  30,000  to  37,000  cubic  feet. 

•Grate  area  of  producer 7  square  feet  per  retort. 

Costs. — Complete  bench,  including  foundations, 
coal-handling  plant,  and  coke-handling  plant, 
but  exclusive  of  house About  £150  per  ton  of  coal  per  max.  diem, 

according  to  size  of  plant. 
Cost  of  house,  with  foundations  (per  ton  of 

coal  per  max.  diem)     .      .      .      .      .      .      .     About  £30. 

Power  required 3  b.h.p.  for  extractor. 

Strictly  speaking,  no  clinkering  is  required  with  the  latest  form  of  producer  fitted 
with  stepped  grate.  Pricking-up  and  removal  of  ashes,  however,  is  carried  out 
every  eight  hours.  The  retorts  are  heated  in  a  series  of  superimposed  chambers 
and  the  heats  can  be  varied  at  will.  The  chambers  are  divided  into  three  :  the  top  or 
waste-gas  circulating  chambers,  the  middle  or  heating  chambers,  and  the  bottom 
•or  regenerator  chambers. 

THE   INTERMITTENT  (DESSAU)  SYSTEM 

This  system,  which  hails  from  the  Continent,  owes  its  inception  to  Dr.  Bueb, 
who  took  out  his  first  patent  in  1902.  In  this,  special  apertures  were  introduced  for 


FIG.  60.— THE  DESSAU  INTERMITTENT  VERTICAL  RETORT  SYSTEM. 

109 


110 


MODERN   GASWORKS   PRACTICE 


taking  off  the  gas  from  the  side  of  the  retort.  Two  years  later  these  side  outlets 
were  dispensed  with,  and  the  system  assumed  the  form,  more  or  less,  in  which  it  exists 
to-day.  In  comparison  with  the  two  previously  mentioned  systems  the  chief  points  to 
notice  are  that  as  the  retorts  are  intermittently  charged  no  continuously  operating 
machinery  is  necessary,  whilst  a  J-inch  steam  pipe  is  provided  at  the  base  for  the  pur- 
pose of  steaming  the  charge  and  increasing  the  gas  yield.  The  steaming,  however, 


FIG.  61. — SCALE  MODEL  OF  INTERMITTENT  SYSTEM. 

is  not  continued  throughout  the  whole  period  of  carbonization  ;  but  with  the  usual 
12-hour  charge  the  supply  is  turned  on  for  the  last  two  hours.  Self -sealing  mouth- 
pieces are  provided  at  both  top  and  bottom  of  the  retort,  and  charging  takes  place 
from  an  overhead  bunker  by  means  of  pouches  drawn  over  the  upper  lids.  An 
interesting  feature  of  the  arrangement  of  gas  take-offs  is  that  a  common  pipe  is 
provided  for  each  row  of  retorts,  and  the  gas  from  the  outer  retorts  passes  through 


VERTICAL   RETORTS   AND   CHAMBER  OVENS       111 

the  mouthpiece  casting  of  those  on  the  side  nearest  to  the  hydraulic  main.  A  com- 
mon spindle  is  employed  for  simultaneously  opening  or  closing  the  lower  lids,  whilst 
a  lever  is  provided  for  tightening-up  the  eccentric  gear  for  ensuring  effective  sealing. 
As  in  the  Glover- West  system,  the  greatest  intensity  of  heating  is  at  the  base  of  the 
retorts.  The  salient  features  of  the  system  are  tabulated  below : — 

Shape  of  retorts Oblong  with  rounded  corners. 

Length  of  retorts 5  metres  (16  feet  5  inches). 

Dimensions  at  top 21  inches  x  8J  inches. 

Dimensions  at  base 27  inches  x  14  inches. 

Number  of  retorts  set  in  each  bed       .      .      .  4  to  18. 

•Coal  carbonized  per  retort  per  24  hours  .      .  22£  cwts.  (12-hour  charges). 

Average  yield  of  gas  (with  steaming)  per  retort 

per  24  hours 15,600  cubic  feet  (12-hour  charge). 

Orate  area  of  producer 19  square  feet. 

Costs. — Complete  bench,  including  founda- 
tions, coal-handling  plant,  coke-handling 

plant,  etc.,  but  exclusive  of  house  .  .  .  £150  per  ton  of  coal  per  max.  diem. 

•Cost  of  house,  with  foundations      ....  £20  per  ton  of  coal  per  max.  diem. 

Make  per  square  foot  of  ground  area  employed 

(outside  dimensions  of  retort  house)  .  .  250  to  350  cubic  feet. 

Owing  to  the  producer  in  this  system  being  of  the  step-grate  design,  clinkering 
in  the  ordinary  sense  is  only  carried  out  about  once  in  every  three  months,  although 
the  fires  are  pricked-up  every  twenty-four  to  forty-eight  hours.  The  formation  of 
hard  masses  of  clinker  is  also  checked  by  judiciously  steaming  the  producer.  To 
:avoid  loss  of  gas  make  from  the  imperfectly  carbonized  portion  of  the  charge  situated 
directly  on  top  of  the  lower  mouthpieces,  a  special  shield  is  provided  to  keep  the 
•coal  away  from  the  door,  and  it  is  usual  to  run  into  the  empty  retort  about  8  inches 
of  breeze  before  admitting  a  fresh  charge  of  coal. 

THE  ELLAND   SYSTEM 

Although  one  of  the  more  recently  introduced  systems,  more  than  half  a  dozen 
installations  of  the  Elland  type  of  verticals  are  now  at  work.  The  retorts  are  de- 
signed to  work  either  continuously  or  with  intermittent  charges,  to  suit  the  require- 
ments of  the  works. 

The  intermittent  system  (Fig.  62)  differs  from  the  continuously  operated  type 
in  that  the  retorts  are  of  considerably  less  total  length.  A  special  feature  is  the 
method  employed  for  ensuring  a  partly  porous  charge  so  that  the  gases  as  they  are 
•evolved  are  provided  with  a  ready  exit.  Unscreened  coal  is  charged  in  a  thin  stream 
against  one  side  of  the  retort,  this  causing  the  nuts  to  accumulate  on  the  one  side 
;and  the  slack  along  that  side  at  which  charging  takes  place.  In  addition  to  ensuring 
a  porous  charge  it  is  claimed  that  a  less  dense  coke  is  produced ;  whilst  the  coal  is 
permitted  to  shrink  freely  from  the  walls  of  the  retort,  and  in  this  way  facilitates 
discharge.  On  charging,  the  flow  of  coal  from  the  hopper  ceases  automatically 
when  the  required  level  is  reached.  The  shoot  is  then  withdrawn,  and  its  contents 
drop  into  the  retort.  The  self -sealing  lids  are  of  special  construction,  a  toggle  system 
•of  levers  being  used  instead  of  eccentrics  ;  and  a  single  pull  by  the  attendant  suffices 


t 


48-Hour  Capacity  Storage  Hoppen 

ior  CoaJ  Ft 


Thete  Charging  Shook  build 
light  poroQB  charges  from  on- 
screened  coal,  waen  the  coal 
reaches  the  thoot  it 

automatically  iU  own  charge. 


Each 

Compartment  of  Setting 
Producer  Gaa  Chamber 
Producer  Gaa  Damper 
to  Each  Burner. 
Separate    Cold    Secondary 
Air  Inlet  to  Regene    ' 
One  Inlet  to  Each  Bi 
Out  Collecting  Chamber 
Step  Grate 


Single  Pull  Self. Sealing  L]d» 
each  Operated  Independently 
'  Hand  Lever  from  Oatndn. 


FIG.  62. — THE  ELLAND  SYSTEM  OF  INTERMITTENT  VERTICAL  RETORTS. 


112 


(rae-TifJ.1  Coal  ana  Coke  Vtin 
at  be  coo.plet.ij  renond. 
thmby  makin<tbbui  Mil- 


******* 

Huiinui  Tipo  wben  Cod  i>  Soeunf. 

Hmjani  Tipo  »bere  Coke  i>  Shjmkii* 


Wute  Be«t 

To  Heal  Satnnlm)  Primary  All 
To  Beat  Secondary  Air  lit  in  Iron  Tube 
2nd  to  Fiieck;  Tone 

Secondary 

^^prunarj»B 
£  P-lMBlti 


50 


SXCTION  OB  H 


I'KIHARY  A1B  — 
SECONDARY  AIB  - 
PRODOCEE  OA8  - 
WiSTI  H1AT  — 


^L 


SECTION  on  BB 


FIG.  63. — THE  ELLAND  SYSTEM  OF  CONTINUOUS  VERTICAL  RETORTS. 

113 


114 


MODERN   GASWORKS   PRACTICE 


to  raise  and  seal  the  lids.  The  regenerators  are  of  the  tubular  type,  and  the  setting 
is  subdivided  in  a  manner  to  give  a  maximum  control  of  the  heats.  The  retorts 
are  usually  set  fifteen  to  a  bed,  are  16  feet  6  inches  long,  and  each  carbonizes  25 
•cwts.  of  coal  per  diem. 

THE  CONTINUOUS   SYSTEM 

The  retorts  in  this  system  are  25  feet  in  length,  and  are  charged  by  means  of  a 
;gas-tight  valve  arranged  with  two  inlets.  One  of  these  inlets  is  for  the  ordinary  pur- 
pose of  charging  in  coal,  the  other  is  for  use  in  the  case  of  those  retorts  which  have 
undergone  scurfing,  and  which  first  receive  a  charge  of  coke.  As  will  be  seen  from 
Fig.  63,  the  coal  is  fed  on  the  centre  line  of  the  retort.  The  taper  of  the  retort  is 
greater  at  the  top  than  at  the  bottom  ;  this  is  to  accommodate  for  expansion  of  the 
coal  on  first  heating.  There  are  no  stationary  inclines  or  curved  parts  to  support 
the  charge,  which  during  its  downward  travel  meets  successively  larger  cross-sections, 
until  the  extractor  gear  is  reached.  This  actually  supports  the  maximum  cross- 
section  of  the  charge,  hence 
bridging  or  hanging-up  is 
prevented.  At  the  base  of 
the  retort  is  an  inclined 
plate  supporting  the  whole 
charge  at  the  natural  angle 
of  repose,  and  the  coke  is 
gradually  pushed  off  by  the 
reciprocating  motion  of  the 
plate,  which  makes  one 
complete  stroke  in  about 
seven  minutes.  The  coke 
is  cooled  by  circulating 
primary  and  secondary  air  around  the  base  of  the  retorts,  which  are  heated  on 
their  broad  sides  only.  Each  retort  is  provided  with  independent  secondary-air 
supply,  producer-gas  and  waste-gas  dampers ;  so  that  individual  control  of  heats 
is  ensured.  The  retorts  are  built  up  from  special  moulded  blocks5  and  each  is 
rated  to  carbonize  5  tons  of  coal  per  day,  four  retorts  being  laid  in  each  bed. 
The  continuous  retorts  are  approximately  5  feet  wide  by  18  inches  broad  at  the 
bottom,  this  being  reduced  to  4  feet  by  10  inches  at  the  top. 

THE   GLASGOW  SYSTEM 

This  system,  designed  by  Mr.  Alexander  Wilson,  was  introduced  for  the  pur- 
pose of  dealing  with  the  non-caking  or  semi-caking  Scotch  coals,  which  under  ordinary 
circumstances  give  a  particularly  small  and  friable  coke.  So  far  the  installations 
have  been  chiefly  confined  to  Scotland,  and  plants  are  at  present  at  work  at 
Glasgow  (5  million  cubic  feet  per  day),  Johnstone,  Alloa,  and  Arbroath.  In  order 
that  the  charge  may  have  ample  time  to  consolidate,  the  coke  is  not  drawn  out 
continuously,  but  at  intervals  of  about  four  hours.  In  this  way  a  fairly  large  coke 


SECTION  ON  CC  (Fie.  63) 
FIG.  63 A. 


FIG.  64. — THE  GLASGOW  VERTICAL  RETORT  SYSTEM. 


115 


116  MODERN   GASWORKS   PRACTICE 

of  good  appearance  is  obtained.  The  quantity  of  coke  extracted  at  each  period  of 
discharging  is  governed  by  the  size  of  the  wagon  or  shoot  into  which  it  is  delivered ; 
this  is  due  to  the  fact  that  as  the  receiving  wagon  fills  up  it  supports  the  whole 
weight  of  the  charge  in  the  retort,  the  bottom  mouthpiece  when  being  closed 
cutting  through  the  coke  column  and  sealing  the  base  of  the  retort.  No  constantly 
moving  machinery  is  required,  and  the  coke  is  cooled  in  the  bottom  cast-iron  cham- 
bers, to  which  are  attached  movable  buckets  for  holding  the  water  seals.  These 
buckets  are  actuated  by  a  small  hydraulic  ram,  so  that  the  movement  of  the  handle 
of  the  water  cock  serves  to  push  back  the  bucket,  allowing  the  requisite  quantity 
of  coke  to  fall  into  the  receiving  wagon.  Another  movement  of  the  handle  then 
closes  the  bucket,  which  is  sealed  in  water  to  render  it  gastight.  The  retorts,  which 
are  rectangular  in  section,  are  built  up  of  tongued  and  grooved  bricks,  and  vary  in 
length  according  to  the  size  of  the  installation.  They  are  built  with  the  whole  of  the 
taper  at  the  top  third  of  the  length,  the  bottom  two-thirds  being  parallel.  For  this 
construction  it  is  claimed  that  unless  the  deposit  of  "  scurf  "  is  allowed  to  get  very 
heavy  there  is  no  trouble  with  the  holding-up  of  the  charge  when  the  retorts  are 
drawn.  The  charging  of  the  coal  into  the  retort  is  effected  by  opening  a  large  cock 
or  valve  having  an  upright  plug,  the  lower  opening  of  which  connects  with  the 
retort  and  the  upper  opening  with  the  coal  hopper.  The  amount  of  free  space  in  the 
retort  (usually  about  3  per  cent,  of  the  total  volume)  is  regulated  by  a  rod  which 
projects  into  the  top  of  the  retort  for  the  required  distance.  The  movement  of  this 
rod  indicates  when  the  proper  quantity  of  coal  has  been  delivered,  and  the  charging 
cock  is  then  closed.  For  the  benefit  of  the  quality  of  the  coke  the  coal  charge 
may,  if  desired,  be  subjected  to  a  small  amount  of  steaming.  The  producers,  which 
are  fed  with  cold  coke,  are  carried  right  up  to  the  top  of  the  setting,  this  giving  an 
ample  reserve  of  fuel,  and  thereby  minimizing  the  amount  of  attention  required. 
The  producer  gas  is  admitted  around  the  upper  portions  of  the  retort,  so  that  the 
maximum  heat  is  concentrated  here ;  the  gases  then  circulate  downwards,  leaving 
the  setting  at  the  base.  The  coal  hoppers  are  of  large  capacity  in  order  to  allow 
for  sufficient  storage  to  carry  the  work  over  Sundays  without  refilling.  The  following 
are  the  more  important  features  in  connexion  with  the  design  of  the  system  : — 

Retorts :  Length .  .      .      ..    20  or  23  feet, 

Breadth  and  width.     At  top  .     .      .40  inches  by  10  inches. 
At  base      .      .     48  inches  by  18  inches. 
Coal  carbonized  per  retort  per  24  hours  .      .     3  tons. 
Average  yield  per  retort  per  diem.      .     .      .     31,500  to  37,500  cubic  feet,  according  to  class 

of  coal. 
Number  of  retorts  in  each  setting  .     .     •     .     4,  6,  or  10. 

Grate  area  of  producer 4  square  feet  per  retort  per  bed. 

Approximate  time  taken  by  coal  in  travelling 
from  entrance  into  and  exit  from  retort    .     18  hours. 

HERRING'S   SYSTEM 

Mr.  W.  R.  Herring's  system  of  vertical  retorts,  erected  at  Edinburgh,  differs  from 
the  majority  of  installations  at  work  in  this  country  in  that  the  retorts  are  fired  by 


VERTICAL   RETORTS   AND   CHAMBER   OVENS       117 


means  of  outside  producers.  The  system  may  be  worked  on  either  the  continuous 
or  intermittent  principle.  When  working  continuously  the  coke  extractor  is 
devised  to  act  as  a  cutter,  wherewith  the  size  of  the  coke  is  reduced  as  required.  The 
retorts,  which  are  built  up  of  tongued  and  groov.ed  bricks,  are  of  rectangular  shape, 
and  receive  their  coal  charge  through  a  special  closure  apparatus  (Fig.  65)  which  is 
designed  to  maintain  a  gastight  joint  while  permitting  the  passage  of  the  coal.  The 


FIG.  65. — HERRING'S  COAL-FEEDING  DEVICE. 


•'*'* 33j8fc •5ii^iv?iS^SkJ?&'fi,-i-«'-ifesk'*f> **-"*•  --  ->;<fc":5 


FIG.  66. — HERRING'S  COKE  EXTRACTOR. 


FIG.   67. — HERRING'S  SYSTEM   OF  VERTICAL 
RETORTS. 


coal  then  finds  its  way  into  the  retort  through  an  upper  cylindrical  pouch,  to  which 
the  gas-outlet  is  also  affixed.  The  coke  extractor  (Fig.  66)  is  varied  in  speed  in 
accordance  with  the  class  of  coal  undergoing  carbonization,  and  the  coke  on  pass- 
ing this  is  confined  in  special  chambers,  where  it  is  slowly  quenched.  The  outlet 
of  the  coke  hopper  is  closed  by  a  special  gastight  device  similar  to  that  through 
which  the  coal  is  admitted  to  the  retort.  Heating  of  the  retorts  takes  place  from 
the  top  downwards,  so  that  the  newly  charged  coal  passes  at  once  into  the  highest 


118  MODERN   GASWORKS   PRACTICE 

temperature  zone.  Pyrometric  tests  conducted  by  Mr.  Herring  showed  that  the 
temperature  varied  from  2,064°  Fahr.  towards  the  top  to  1,562°  Fahr.  at  the  base. 
The  following  are  the  more  important  particulars  connected  with  the  installation  : — 

Shape  of  retorts    ......"..  Rectangular. 

Total  length      .      .      .      .     '.      .      .      .      .      .25  feet. 

Breadth  and  width  :    Top 39  inches  by  11  inches. 

Base 48  inches  by  20  inches. 

Coal  carbonized  per  retort  per  24  hours  .      .  70  cwts.  Scotch  common  coal. 

Average  yield  per  retort  per  24  hours      .      .  38,000-39,000  cubic  feet. 

Number  of  retorts  set  in  each  bed      ...  6. 
Capital  cost  for  complete  bench,  exclusive  of 

foundations,  but  inclusive  of  coal-handling 

plant,  coke-handling  plant,  etc.  (house  not 

included) £148  per  ton  of  coal  per  max.  diem. 

Make  per  square  foot  of  ground  area  .      .      .  370  cubic  feet  per  diem. 

The  outside  producers  are,  of  course,  fed  with  cold  coke  and  are  subjected  to 
steaming.  The  free  space  in  the  retort  is  adjustable  at  will  by  regulation  of  the 
coal  feed  ;  and  the  gas  is  taken  off  to  a  dry  main.  The  approximate  time  occupied 
by  the  coal  in  travelling  from  the  top  to  the  base  of  the  retort  is  twenty-four  hours. 

THE   HOLMES-WINSTANLEY  SYSTEM 

The  Holmes- Winstanley  system  has  many  unique  features,  which  have  been 
introduced  to  simplify  as  much  as  possible  both  the  construction  and  operation  of 
vertical  retorts.  The  first  installation  on  this  principle  was  erected  by  Mr.  Alex- 
ander Waddell,  of  Dunfermline. 

These  retorts  may  be  arranged  so  as  to  discharge  continuously  by  a  power 
operated  device  or  (as  is  preferable  in  small  installations)  at  convenient  intervals  by 
hand.  Fig.  68  shows  a  cross-section  of  the  setting.  The  coal  is  fed  into  a  hopper 
which  is  in  direct  communication  with  the  retort  and  holds  a  twenty-four  hours' 
supply  of  coal.  This  is  a  feature  peculiar  to  this  system.  The  hopper  may  be 
fed  from  small  hand-propelled  bogies,  telpher  skips,  or  travelling  hoppers,  as  may 
be  convenient.  A  patented  feeding  door  is  provided  in  the  top  of  the  hopper,  which 
engages  automatically  with  the  bogie,  skip,  etc.,  on  the  latter  being  brought  into 
position  over  the  hopper,  and  opens  and  closes  without  allowing  any  escape  of  gas. 
The  contents  of  the  retort,  as  will  be  seen  from  the  sketch,  are  under  constant 
pressure  from  the  column  of  coal  in  the  hopper,  the  "  free  space  "  being  practically 
confined  to  a  small  pocket  formed  at  the  gas  outlet. 

By  this  arrangement  the  formation  of  dust  is  avoided  and  the  gas  has  to  pass 
through  a  considerable  area  of  comparatively  cold  coal  before  leaving  the  retorts. 
The  coal  in  the  hoppers  may  be  replenished  at  any  convenient  intervals,  or  the 
hoppers  may  be  filled  up  once  only  during  the  twenty-four  hours.  In  cases  where 
heavily  coking  or  small  coal  is  intended  to  be  carbonized,  it  has  been  found  to  be 
an  advantage  to  provide  an  auxiliary  gas  take-ofE  about  half-way  down  the  retort. 

In  the  original  design  (having  chiefly  in  view  the  requirements  of  medium  sized 
and  small  works),  as  easy  a  means  of  taking  away  the  coke  as  possible  without  the 


VERTICAL   RETORTS   AND   CHAMBER   OVENS       119 


assistance  of  constantly 
moving  machinery  was  con- 
sidered necessary,  and  it  was 
decided  that  this  could  be 
effected  by  bringing  the  dis- 
charging point  well  to  the 
outside  of  the  structure  by 
adding  a  "  right  angle " 
shaped  chamber  to  the  retort 
proper,  with  a  mouthpiece  in 
the  outer  wall  of  the  setting. 
The  mouthpiece  lid  being 
open,  the  coke  may  be  re- 
ceived into  a  tipping  wagon, 
skip,  or  conveyor,  as  the  case 
may  be.  The  wagon  is  most 
suitable  for  small  installa- 
tions, and  the  amount  of  coke 
withdrawn  may  be  more 
easily  regulated  by  this 
means.  A  safety  door  is 
fitted  inside  the  discharging 
chamber,  actuated  by  a 
hand- lever,  by  means  of 
which  the  flow  of  coke  from 
the  mouthpiece  may  be  con- 
trolled, or  stopped  altogether, 
as  desired.  The  discharging 
chamber  and  the  lower  por- 
tion of  the  retort  together 
constitute  a  cooling  chamber 
for  the  coke. 

For  large  installations  a 
continuous  discharge  operated  coke  Track 
by  power  is  provided  for, 
wherein  a  sliding  pusher 
enters  alternately  the  inner 
end  of  the  retorts,  set  back 
to  back,  pushing  the  coke 

forward  to  a  receiving  cham-       Fm    68._THE  HOLMES-WINSTANLEY  VERTICAL    RETORT 
ber,    which    takes  the   place  SYSTEM. 

of   the    mouthpiece    in    the 

outer    wall    of    the    setting.     By   means    of  a  movable  shoot   the   furnaces   are 
charged  direct  from  the  retorts  on  one  side  of  the  setting.      The  clinkering  of  the: 


Coke  Truck. 


120  MODERN   GASWORKS   PRACTICE 

producer  is  effected  at  the  inner  side,  in  the  space  between  the  supporting  walls  of 
the  setting. 

The  Holmes- Winstanley  retort  is  heated  by  means  of  a  series  of  horizontal  com- 
bustion chambers  arranged  between  the  side  walls  of  the  retorts.  The  gases  rising 
from  the  producer  meet  the  secondary  air  in  the  bottom  chamber  and  pass  upwards 
through  the  combustion  chambers  to  the  stack.  Ports  and  baffles  are  arranged  in 
each  chamber  so  that  the  combustion  may  be  controlled  to  suit  the  heat  require- 
ments at  any  point  in  the  retort,  from  outside.  Separate  steel  chimneys  are  pro- 
vided for  each  setting.  The  retorts  may  be  arranged  in  settings  of  2's  or  4's.  There 
are  no  special  bricks  employed  in  the  construction  of  the  retorts. 

In  small  works  the  power  and  machinery  necessary  to  elevate  the  coal  to  the 
desired  height  is  the  most  serious  problem  to  be  considered  when  installing  verticals. 
The  provision  of  the  large  hoppers  with  these  retorts  renders  overhead  bunkers 
on  small  installations  unnecessary,  and  by  using  coal  bogies  holding,  say,  one  ton 
of  coal,  a  lift,  either  hydraulic  or  electrical,  is  all  that  is  required  to  handle  the  coal. 
Coal  breakers,  storage  bunkers,  etc.,  on  the  ground  floor  may  be  arranged  to  com- 
municate direct  with  the  foot  of  the  lift  well. 

KOPPERS'   CHAMBER  OVENS 

These  ovens  have  been  extensively  adopted  on  the  Continent  for  gasworks 
carbonization,  and  a  large  installation  is  at  work  in  this  country  at  the  Saltley  works 
of  the  Birmingham  Corporation.  So  far  as  the  quality  of  coke-oven  gas  is  concerned, 
this  can  be  said  to  compare  very  favourably  with  coal  gas  so  long  as  the  practice 
of  benzol  "  stripping  "  is  avoided.  In  Germany  the  distribution  of  coke-oven  gas 
has  been  carried  out  on  a  comparatively  large  scale,  one  of  the  chief  centres  being 
Waldenberg,  which  provides  for  the  greater  part  of  the  Silesian  Plain  by  means  of 
long-distance  transmission  systems.  At  Miilheim  the  company  guarantee  a  mini- 
mum calorific  power  of  600  B.Th.U.  per  cubic  foot,  but  in  this  case  only  the  por- 
tion of  the  gas  evolved  during  the  most  favourable  period  of  carbonization  is  diverted 
for  town's  purposes.  So  far  as  this  country  is  concerned,  a  certain  amount  of  caution 
has  been  displayed  in  the  adoption  of  the  gas,  though  recent  converts  are  the  towns 
of  Middlesbrough  and  Leeds,  where  a  supply  is  taken  from  the  adjacent  ovens.  As 
regards  the  transmission  of  the  gas,  it  seems  to  lose  little  of  its  value  in  travelling 
long  distances,  and  in  Germany  pipe- lines  of  great  length  have  been  laid. 

In  the  Birmingham  installation  of  Koppers'  chamber  ovens  the  ovens  them- 
selves are  35  feet  long,  8  feet  10  inches  high,  and  taper  in  width  from  19|  inches  to 
18  inches.  Each  is  capable  of  taking  a  charge  of  from  eight  to  ten  tons  of  coal,  the 
average  period  of  carbonization  being  twenty-four  hours.  The  arrangement  of 
regenerators  (Fig.  70)  is  unique,  each  oven  being  supplied  with  its  separate  system, 
consisting  of  a  chamber  (C)  divided  vertically  into  two  compartments.  The  secondary 
air  flows  through  one  of  these  chambers  and  the  gas  through  the  next,  and  so  on  ; 
the  two  meeting  at  the  bottom  of  a  vertical  combustion  chamber  (E)  extending  to  very 
nearly  the  same  height  as  the  oven.  The  products  of  combustion  then  pass  into 
a  common  horizontal  flue  (G),  over  a  parting  wall,  and  down  vertical  flues  similar  to 


121 


122 


MODERN   GASWORKS   PRACTICE 


the  combustion  chambers,  thence  to  the  regenerators  and  main  flue.  By  means  of  a 
special  change-over  gear  an  interchange  is  effected  between  the  preheating  chambers 
of  producer  gas  and  secondary  air  ;  that  is  to  say,  the  air  is  admitted  to  those  cham- 
bers previously  taking  gas,  and  vice  versa.  In  this  way  the  preheating  of  both  air 
and  gas  is  arranged  for,  the  change-over  taking  place  about  every  half-hour.  In 
the  majority  of  these  plants  the  gas  from  the  ovens  themselves  is  used  for  main- 
taining the  working  heats  ;  but  in  the  Birmingham  installation,  as  before  explained, 
the  heating  is  carried  out  by  means  of  low-grade  gas  from  a  Mond  producer.  The 
regulation  of  the  gas  to  each  chamber  is  arranged  for  by  means  of  adjustable  metal 


f-  *  » 

I*  I  I 


. 


'    "  *        -> 


mm    mm    a  a    s 

FIG.  70. — KOPPERS'  REGENERATOR  SYSTEM. 


cocks,  and  the  quantity  passing  forward  is  also  dependent  upon  the  pressure  from 
the  Mond  producers.  For  the  production  of  a  dense  metallurgical  coke  the  coal 
is  first  ground  in  a  special  form  of  disintegrator  to  a  fine  dust,  and  is  then  delivered 
to  the  "  stamping  machine,"  where  it  is  compressed  into  a  solid  cake  of  practically 
the  same  dimensions  as  the  oven,  and  introduced  through  the  end  door.  For  many 
purposes  unstamped  coal  may  be  made  use  of,  in  which  case  charging  takes  place 
by  means  of  a  machine  running  along  the  top  of  the  settings  and  discharging  through 
hoppers  into  three  openings  in  the  roofs  of  the  chambers.  The  coal  is  afterwards 
levelled  by  a  machine  travelling  alongside  the  setting,  the  latter  machine  being  also 
provided  with  a  ram  for  the  purpose  of  discharging  the  coke  at  the  end  of  the  car- 


123 


124 


MODERN   GASWORKS   PRACTICE 


bonization  period.  The  operation  of  discharging  usually  takes  about  five  minutes. 
The  self-sealing  oven  doors  are  cooled  by  a  water  circulating  arrangement  round 
the  frame  of  the  door. 

MUNICH  CHAMBERS 

A  noteworthy  system  of  carbonization  in  bulk  wThich  is  finding  its  way  into 
this  country  is  the  chamber-oven  plant  designed  by  Herr  Hies,  of  the  Munich  gas- 


FIG.  72. — MUNICH  CHAMBER  OVEN  SYSTEM. 


•works.  The  chamber  consists  of  a  tapered  inclined  coke  oven.  There  are  three  or 
more  of  these  in  each  setting,  set  at  angles  varying  from  40°-42°  with  the  horizontal. 
They  are  constructed  from  special  keyed  bricks  and  charged  from  an  opening  on 
the  top  of  the  beds.  Coal  is  elevated  to  continuous  overhead  hoppers  and  directed 


VERTICAL   RETORTS   AND   CHAMBER   OVENS       125 

into  the  ovens  by  means  of  a  special  shoot.  Some  idea  of  the  rapidity  of  charging  can 
be  gained  from  the  fact  that  in  the  most  recent  installations  only  twenty-five  seconds- 
is  required  for  the  complete  filling  of  a  chamber  taking  from  seven  and  a  half  to  eight 
tons.  Owing  to  the  moderately  sharp  incline  at  which  the  chambers  are  set,  the 
coke  will  in  many  cases  discharge  itself  without  any  outside  assistance,  but 
in  order  that  any  tendency  to  hang  up  may  be  avoided,  a  light  starting-ram  is- 
provided  to  set  the  carbonized  charge  in  motion.  The  discharger  consists  of  a  light 


FIG.    73.— BENCH 


MUNICH   CHAMBER   OVENS   SHOWING  COKE-QUENCHING  MACHINE. 


"  link-coiling  "  ram  geared  to  an  electric  motor  ;  and  the  pusher,  by  means  of  suit- 
able guides,  is  constrained  to  move  in  a  straight  line,  following  the  angle  of  the  oven 
which  it  enters.  As  a  general  rule  the  complete  charge  is  dispatched  in  about  forty 
seconds.  The  oven  doors,  which  are  extremely  massive,  are  raised  by  an  electric 
hoisting  motor,  and  the  incandescent  coke  runs  direct  into  a  specially  designed 
coke- quenching  machine.  The  chamber  door  is  then  lowered,  and  automatically 
engages  itself  in  a  special  fastener  for  ensuring  a  hermetical  seal.  In  the  Munich 
installation  the  coke-quencher  consists  of  a  mild-steel  receiving  hopper  surmounted 


126  MODERN  GASWORKS   PRACTICE 

by  a  ferroconcrete  shaft  of  square  section  .for  the  purpose  of  conducting  the  steam 
to  a  considerable  height  before  its  escape  into  the  air  is  permitted.  After  quench- 
ing has  been  partly  carried  out  by  means  of  a  spray  at  the  head  of  the  hopper  the  . 
coke  goes  into  a  swing-boat  conveyor,  cased  with  steel  plates,  which  scrapes  it 
through  a  bath  of  water  and  delivers  it,  fully  quenched,  to  a  de  Brouwer  con- 
veyor. The  coke  is  then  carried  on  to  a  screening  and  sorting  plant.  Outside  pro- 
ducers have  in  some  instances  been  employed  for  heating  the  ovens  ;  but,  in 
general,  each  bench  ,of  three  is  provided  with  a  self-contained  producer,  the  fuel 
consumption  averaging  from  14  to  15  per  cent,  of  the  coal  carbonized.  A  feature 
of  the  producer  is  the  water-cooled  grate,  which,  in  conjunction  with  the  steam- 
ing employed,  practically  obviates  ordinary  clinkering.  At  the  Altona  works 
at  Hamburg  a  plant  was  put  to  work  in  November,  1913,  and  between  then 
and  the  end  of  March,*  1914,  clinkering  was  only  resorted  to  on  one  occasion. 
The  furnaces  do,  however,  require  some  attendance,  and  "  pricking-up  "  is  regu- 
larly carried  out  every  eight  hours.  Any  class  of  coal  can  be  charged  into  the 
ovens  so  long  as  the  lumps  do  not  exceed  10  x  15  inches  in  size.  Much  depends, 
however,  on  the  type  of  coke  required.  For  a  semi-coke  the  temperature  of 
carbonization  is  kept  down  to  1,100°  Fahr.  ;  whilst  for  furnace  coke  the  coal  is 
ground  extremely  fine,  carbonized  at  2,000°  Fahr.,  and  steamed  in  the  bunkers 
with  exhaust  steam  so  as  to  add  the  requisite  10  per  cent,  of  moisture.  At  the  Tegel 
works,  Berlin,  there  are  eighty-one  of  these  ovens  at  work,  carbonizing  567  tons  of 
coal  per  diem.  An  idea  of  the  labour  entailed  can  be  gleaned  from  the  fact  that 
eighteen  men  are  required  for  an  output  of  7,000,000  cubic  feet  in  twenty-four 
hours.  At  the  Moosah  gasworks,  Munich,  there  are  now  eighty-seven  ovens  at 
work. 

The  salient  features  of  the  Munich  chamber  system  are  given  below  : — 

Shape  of  chamber.      .  ' Rectangular  tapered. 

Slope 40-42°  with  horizontal. 

Length   .  26  feet  (actual  length  of  sloping  floor  line). 

Mean  width  \ 1  foot  9  inches. 

Height 9  feet  10  inches. 

Coal  carbonized  per  chamber  per  24  hours .      .     2  J  to  8  tons,  as  desired. 
Average  yield  of  chamber  per  24  hours    .      .     100,000  cubic  feet. 
Number  of  chambers  set  in  a  bed.      .      .      .     2,  3,  4,  or  5. 

Duration  of  charge 24  hours. 

Grate  area  of  setting 8  to  16  square  feet. 

Costs. — Complete  bench,  including  foundations, 

coal-handling  plant,  power-operating  plant, 

coke-handling  plant,  etc.,  but  exclusive   of 

building £230  per  ton  of  coal  per  diem. 

Cost  of  housing .      .      .     £5  to  £9  per  ton  of  coal  per  diem. 

Working  charges    .      -.      . \\d.  to  3d.  per  ton  of  coal,  according  to  size  of 

installation. 

NORWICH  CHAMBERS 

At  a  time  before  the  merits  of  the  fully  charged  horizontal  retort  were  realized 
Mr.  Thos.   Glover  introduced  at  Norwich  a  special  form  of  semi-chamber  retort. 


VERTICAL  RETORTS   AND   CHAMBER   OVENS       127 

'These  chambers,  which  were  21  feet  long,. 3  feet  high,  and  1  foot  wide,  were  fully 
charged  by  means  of  a  de  Brouwer  projector.  The  average  coal  charge  amounted 
to  21  cwts.,  and  was  distilled  for  a  period  of  twelve  hours.  Compared  with  partly 
filled  horizontals  the  results  were  a  decided  improvement,  but  it  was  eventually 
found  that  heavily  charged  horizontal  retorts  of  the  normal  size  gave  equally 
satisfactory  yields,  and  the  system  was  ultimately  abandoned. 


128 


HORIZONTAL 
BENCH  . 

WOODALL-DUCKHAM 
VERTICALS. 

GLOVER-WEST 
VERTICALS. 

Intermittent. 

Continuous. 

Continuous. 

Shape  of  retort  

Q 

Rectangular,  tapered 

Oval 

Dimensions  —  Length       *  . 

20  feet 

25  feet 

19  to  25  feet 

Breadth  and  width-  —  Top    

24  inches  x  16  inches 

3  ft.  10J  in.  x  8  in. 

From  27  in.  x  12  in. 

to  33  in.  x  8  in. 

„                 „            Bottom              % 

Do. 

5  ft.  3  in.  x  18J  in. 

From  36  in.  x21  in. 

•    • 

to  39  in.  x  18  in. 

Coal  carbonized  per  retort  per  24  hours  . 

1£  tons 

4^  to  5^  tons  l 

2J  to  3J  tons 

Yield  per  retort                                  „ 

20,000  cubic  feet 

60,000  to  70,000 

35,000  to  40,000 

cubic  feet  J 

cubic  feet 

No.  of  retorts  set  in  each  bed     -  .      .      , 

8  to  12 

2  or  4 

Usually  8 

Duration  of  charge  ....... 

8  to  12  hours 

Continuous 

Continuous 

Grate  area  per  setting  

20  square  feet 

7  square  feet 

7  square  feet 

per  retort 

per  retort 

Producer  charged  with       

Hot  coke 

Cold  coke 

Cold  coke 

Is  coal  charge  steamed?    .      .      . 

No 

No 

No 

Average  yield  per  square  foot  of  ground 

' 

area  per   diem  (outside  dimensions  of 

t 

house)  

200  to  250  cubic  feet 

350  to  475  cubic  feet2 

400  cubic  feet 

Capital  costs  (complete  bench,  including 

foundations,  coal-handling  plant,  power- 

operating    plant,   coke-handling   plant, 

but  exclusive  of  house,  per  ton  of  coal 

per  maximum  day)    

£110  to  £140  2 

£140  to  £180  2 

£150  to  £170  2 

Cost  (as  above)  per  1,000  cubic  feet  per 

. 

maximum  day       

£9-5  2 

£10  to  £14  2 

— 

Cost  of  house  (with  foundations)  per  ton 

£45  to  £65,  inclusive 

£25  to  £45,2  ex- 

£30,2 exclusive  of 

i 

of  coal  per  maximum  day      . 

of  3  weeks'  coal 

clusive  of  coal  stores 

coal  stores 

storage 

Working  costs  per  ton  of  coal  (total  labour 

in  retort  house)      .      .      .      .      •. 

Is.  to  Is.  6d.5 

7^d.2 

4Jd.  to  6dL2 

Approximate  time    occupied  by  coal  in 

travelling  from  entrance  to  exit  of  retort 

— 

7  to  8  hours 

12  hours 

Speed  of  coke  extractor      .      .      .      ... 

— 

1  revolution  in  50 

1  revolution  in  30 

to  70  minutes  1 

to  40  minutes  1 

Coke  quenched  

<    Water  spray 

By  primary  air  cir- 

By secondary  air 

culating  round 

circulating  round 

base  of  retort 

base  of  retort 

Method  of  heating          

Equal  distribution 

Top  heating 

Bottom  heating 

Gas  take  off    : 

Wet  or  dry  main 

IT                       o 

Wet  main 

Dry  main 

3  Scotch  common  coal. 
N.B. — All  costs  (both  for  capital  and  labour)  given  above  are  liable  to  considerable  variation  in.i 


1  According  to  class  of  coal  carbonized.  2  According  to  size  of  plant. 

4  This  is  exclusive  of  foundations.  5  In  exceptional  cases  as  low  as  9rf. 


VERTICAL   RETORTS   AND   CHAMBER  OVENS 


129 


SYSTEMS  OF  CARBONIZATION. 


DESSAU 
VERTICALS. 

GLASGOW 

VERTICALS. 

HERRING'S 
VERTICALS. 

KOPPERS  ' 
CHAMBER  OVENS. 

MUNICH 
CHAMBERS. 

Intermittent. 

Continuous-inter- 

Continuous. 

Intermittent. 

Intermittent, 

mittent. 

Oblong  with  round            Rectangular 

Rectangular 

Rectangular, 

Rectangular, 

corners 

tapered 

tapered 

5  metres  (16  ft.  5  in.)         20  or  23  feet 

25  feet 

35  feet 

26  feet 

21  inches  x  8£  inches    40  inches  x  10  inches 

39  inches  x  1  1  inches 

Width,  18  inches  to 

Mean  width,  21  inches 

19£  inches 

27  inches  x  14  inches    48  inches  x  18  inches 

48  inches  x  20  inches 

Height  8  feet  10 

Height, 

inches 

9  feet  10  inches 

22£  cwts. 

3  tons 

3£  tons  3 

8  to  10  tons 

2  to  8  tons 

15,600  cubic  feet 

31,500  to  37,500 

39,000  cubic  feet 

100,000  to  120,000 

100,000  cubic  feet 

cubic  feet  *• 

cubic  feet 

4  to  18                        4,  6,  and  10 

6 

— 

2,  3,  4,  or  5 

12  hours                Portion  of  coke 

Continuous 

24  to  30  hours  « 

24  hours 

drawn  every  4  hours 

5  square  feet 

4  square  feet  per 

External  producer 

External  producer 

16  square  feet 

per  retort 

retort 

Cold  coke 

Cold  coke 

Cold  coke 

Slack  coal  or 

Cold  coke  or  fine 

mixture 

breeze 

Steamed  for  last 

Yes,  if  desired 

No 

Wet  coal  carbon- 

No 

2  hours 

ized  if  desired, 

otherwise  no 

250  to  350  cubic  feet  2 

350  to  400  cubic  feet 

370  cubic  feet 

— 

500  cubic  feet 

£150  2 

£142  2 

£148  4 

£180  2 

£230  2 

£10'7  2 

£11-5  2 

£13-5  4 

£14 

£18  2 

£20,  2  exclusive  of 

£23.  2  exclusive  of 

— 

— 

£5  to  £9,  exclusive 

coal  stores 

coal  stores 

of  coal  stores 

4rf.  to  6d.2 

3rf.7 

— 

8d.  to  10d.2 

\\d.  to  3d.2 



18  hours 

24  hours 





— 

Coke  drawn  every 

— 

— 

— 

4  hours 

Water  spray 

Cooled  in  bottom 

Slowly  cooled  in 

Water  spray 

Water  spray 

chamber 

bottom  chambers 

Bottom  heating 

Top  heating 

From  top  down- 

Equal distribution 

Equal  distribution 

j 

wards 

Wet  or  dry  main                Wet  main 

Dry  main 

Dry  main 

Dry  main 

6  According  to  whether  coal  is  stamped  or  unstamped,  or  wet  or  dry.  7  Carbonization  only, 

accordance  with  the  prevailing  costs  of  material  and  labour,  also  the  size  of  the  installation. 


ONLY  within  comparatively  recent  years  has  the  study  of  various  types  of  fireclays 
and  their  relative  merits  for  retort  bench  and  other  purposes  received  more  than 
passing  attention  from  the  gas  engineer.  The  developments  of  present-day  research, 
however,  has  been  the  means  of  creating  a  new  science,  with  the  result  that  refractory 
materials  and  their  application  have  become  one  of  the  most  significant  branches 
of  modern  gasworks'  practice.  Detailed  discussion  of  the  origin  of  clays  is  without 
the  scope  of  the  present  book,  but  it  is  proposed  to  consider  the  question  in  a 
more  or  less  practical  manner,  with  special  reference  to  those  features  by  which 
the  designer  and  purchaser  should  be  influenced. 

The  word  "  refractory  "  in  reality  is  merely  a  comparative  term,  and  in  the 
literal  sense  means  "  unable  to  melt."  A  wide  range  of  substances  is  included  under 
the  classification  of  refractory  materials ;  among  these,  in  addition  to  the  more 
common  types  of  fireclays,  being  carborundum,  alundum,  diamantin,  quartz,  etc. 
No  material  is  completely  refractory ;  that  is  to  say,  all  so-called  refractory  sub- 
stances are  capable  of  fusion,  but  their  respective  yielding  points  are  abnormal  in 
comparison  with  prevailing  working  temperatures. 

Stated  in  brief,  fireclays  are  the  result  of  the  decomposition  of  the  feldspathic 
constituents  of  particular  rocks  subjected  for  untold  years  to  the  destructive  in- 
fluence of  weathering.  Differing  degrees  of  the  process  of  weathering  account  for 
modifications  in  the  type  of  clay  produced,  and  only  in  rare  instances  is  the  process 
so  complete  that  the  final  stage  (i.e.,  reduction  to  true  clay  substance,  kaolin  or 
china  clay)  is  reached.  The  evolution  of  the  true  clay  substance  from  the  feldspars 
in  the  presence  of  carbonic  acid  and  water  may  be  chemically  expressed  as  follows  : — 

Al203.K20.2(3Si02)  -f  2H20  +  C02 

=  4Si02  -f  K2C03  +  Al203.2Si02.2H20  (kaolin) 

These  kaolin  clays  are  highly  refractory  but  are  practically  devoid  of  plas- 
ticity ;  they  exist,  however,  in  relatively  small  quantities,  and  the  larger  deposits 
of  fireclays  of  service  to  the  gas  engineer  are  the  result  of  incomplete  or  intermittent 
weathering.  It  should  be  stated  here  that  although,  as  a  general  rule,  the  refrac- 
toriness of  a  substance  may  be  gauged  by  the  proportion  of  silica  it  contains,  this 
proposition  is  by  no  means  beyond  question,  and  definite  combinations  of  silica 
and  alumina  are  more  highly  infusible  than  when  the  latter  gives  way  to  silica. 
In  fact,  certain  experimenters  have  shown  that  alumina  is  rather  more  refractory 

130 


REFRACTORY  MATERIALS  131 

than  silica,  and  that  by  admixing  the  two  so  as  to  give  the  composition  A1203.  2SiO» 
(i.e.,  true  clay  substance,  see  above  equation)  the  most  infusible  product  is  obtained. 
Ordinary  fireclays  may  in  general  be  denoted  by  the  formula — 

Al203.6Si02 

but  in  addition  to  the  silica  and  alumina  they  contain  varying  quantities  of  impurities, 
such  as  oxides  of  calcium,  magnesium,  titanium,  potassium,  sodium,  and  iron.  These 
impurities,  owing  to  their  low  fusibility,  exert  a  most  harmful  influence  on  the 
ultimate  refractoriness  of  the  clay,  and  in  any  case  their  total  content  should  be 
limited  to  4  or  5  per  cent.  Much  depends,  however,  on  the  type  of  clay  in  question, 
and  some  highly  refractory  materials  now  used  contain  as  much  as  4  per  cent,  of 
iron  alone.  Chief  objection  to  impurities  lies  in  the  fact  that  once  they  themselves 
have  set  up  fusion  by  the  formation  of  fusible  silicates  the  remainder  of  the  material 
may  fall  a  victim  to  their  influence,  even  though  the  prevailing  temperature  is  con- 
siderably below  the  normal  fusing  point. 

Many  recent  investigators  into  the  refractoriness  of  clays  have  emphasized 
the  fact  that  ultimate  chemical  analysis  cannot  be  taken  as  a  final  indication  of 
infusibility ;  in  fact,  instances  have  been  quoted  where  clays  having  chemically 
a  model  composition  have  been  known  to  give  defective  articles.  For  this  reason 
it  has  been  suggested  that  the  analysis  should  be  directed  towards  the  presence 
of  the  various  mineralogical  constituents  on  a  subdivision  such  as  the  following  : — 

(a)  True  clay  substance. 

(b)  Quartz. 

(c)  Remnants  of  the  original  mother  rocks. 

The  last-named  component,  containing  the  original  alkaline  impurities,  is,  per- 
haps, of  chief  importance,  and  for  effective  results  should  be  in  the  neighbourhood 
of  2|  per  cent.  In  the  less  siliceous  clays  the  desirable  kaolin  will  average  about 
72  per  cent.,  the  remainder  being  accounted  for  by  quartz,  which  has  a  varying  in- 
fluence, chiefly  dependent  upon  the  quantity  of  impurities  present.  If  the  impurities 
are  on  the  low  side  the  tendency  of  the  quartz  will  be  to  aid  infusibility.  An  im- 
portant feature  in  connexion  with  impurities  is  that  their  influence  is  more  marked 
in  the  presence  of  silica  than  of  alumina ;  hence  deletion,  as  far  as  possible,  from 
the  highly  siliceous  clays  is  imperative.  Calcium  compounds  are  particularly  to  be 
guarded  against,  owing  to  their  tendency  to  act  as  an  extremely  rapid  and  powerful 
flux.  The  ability  of  the  various  compounds  classified  as  impurities  to  act  as  fluxes 
is  in  direct  ratio  to  their  equivalent  combining  weights.  The  most  desirable  means 
of  determining  the  suitability  of  a  material  for  high-temperature  work  is  undoubtedly 
by  a  combination  of  the  ultimate,  rational,  and  mechanical  analyses. 

THE   WINNING   AND   WORKING-UP  OF  FIRECLAYS 

By  far  the  largest  deposits  of  aluminous  fireclays  in  this  country  occur  in  the 
Stourbridge,  Yorkshire,  and  Newcastle  districts.  The  clay  is  generally  found  at  a. 
considerable  distance  below  the  surface,  and  shafts  are  frequently  sunk  to  depths 
of  500  or  600  feet,  or  even  more.  In  winning  the  clay,  care  has  to  be  taken  to  avoid 


132  MODERN   GASWORKS   PRACTICE 

mixing  the  products  from  distinct  seams ;  for  although  the  seams  occur  in  close 
proximity  to  one  another,  their  chemical  constituents  and  properties  are  by  no 
means  similar.  Thus,  a  highly  desirable  substance  may  be  found  adjacent  to  one 
containing  an  abnormal  proportion  of  deleterious  salts.  After  being  brought  to  the 
surface  the  majority  of  clays  undergo  treatment  known  as  "  weathering,"  which  has 
an  important  influence  on  their  suitability  for  future  use.  This  process  is  essential, 
in  that  the  clay  (stacked  in  shallow  heaps  for  some  considerable  period)  is  subjected 
to  thorough  lixiviation,  with  consequent  reduction  of  the  harmful  alkalis,  which 
are  usually  decreased  by  at  least  40  per  cent.  Once  "  weathering  "  is  complete 
the  requisite  quantity  of  "  green  "  clay  is  made  up  by  thoroughly  grinding  together 
definite  proportions  of  the  varying  types  ;  that  is  to  say,  the  clay  from  one  particular 
seam  is  frequently  not  used  by  itself,  but  if  of  the  "  strong  "  or  siliceous  type, 
it  is  mixed  with  a  certain  proportion  of  the  "  mild "  or  aluminous  quality 
until  the  desired  material  is  obtained.  The  material  having  been  moulded  and 
dried  would  then  be  ready  for  burning  in  the  kilns  but  for  the  fact  that  the  "  green  " 
clay  treated  in  this  manner  is  subject  to  considerable  shrinkage,  and  would 
in  addition  provide  a  finished  article  of  too  fine  a  grain  for  high-temperature  pur- 
poses. In  consequence,  not  the  least  important  consideration  in  the  manufacture 
of  fireclay  articles  is  the  preparation  and  admixture  of  "  chamotte  " — a  substance 
known  in  manufacturing  circles  as  "  grog," — which  reduces  the  shrinkage  to  reason- 
able limits  and  opens  out  the  texture  of  the  material,  rendering  it  of  greater  porosity. 
It  is  because  contraction  takes  place  on  burning  that  fireclay  goods  are  rarely  abso- 
lutely consistent  as  regards  size,  for  it  is  impossible  to  foretell  with  perfect  accuracy 
what  the  shrinkage,  or  "  sink,"  will  amount  to.  For  ordinary  Stourbridge  fire- 
bricks the  contraction  on  burning  usually  amounts  to  1  inch  to  1^  inches  per  foot, 
the  length  of  a  9-inch  brick  being  9f  inches  before  burning  ;  whereas  with  gas  retorts, 
the  amount  is  about  f  inch  per  foot,  and  a  finished  retort  measuring  24  inches  by 
16  inches  would  be  moulded  before  burning  to  25J  inches  by  17  inches. 

The  selection  and  preparation  of  "  grog  "  has  to  be  carried  out  with  great  care, 
since  a  superior  clay  may  be  completely  ruined  by  the  careless  introduction  of  an 
inferior  "grog."  " Grog "  is  usually  prepared  from  a  clay  which  originated  in  the  same 
seam  as  the  fireclay  with  which  it  is  to  be  mixed.  This  clay,  in  the  form  of  lumps, 
is  burnt  in  a  kiln  out  of  contact  with  the  fuel ;  and  the  firing  temperature  should 
be  greater,  or  at  least  as  great,  as  that  to  which  the  finished  article  will  be  subjected. 
The  lumps  are  then  ground  to  the  desired  size.  The  quantity  of  "  grog  "  added 
varies,  of  course,  with  the  material  required  and  the  kind  of  clay  made  use  of.  For 
firebricks  and  smaller  articles,  however,  it  is  usually  added  in  a  proportion  of  from 
15  to  20  per  cent.,  while  for  larger  articles,  such  as  retorts,  the  amount  is  increased 
to  from  30  to  40  per  cent. 

On  the  Continent  the  preparation  of  chamotte  is  an  industry  in  itself,  and  lumps 
of  selected  burnt  clay  are  dispatched  long  distances  for  the  use  of  manufacturers. 
In  some  Continental  fireclays  ordinary  "  grog  "  is  dispensed  with,  and  in  its  stead 
a  special  china  clay  is  employed,  the  shrinkage  of  which  is  so  small  that  it  may 
be  used  without  previous  burning. 


REFRACTORY   MATERIALS 


133 


THE   CLASSIFICATION   OF  REFRACTORY  MATERIALS 

Refractory  materials  are,  in  general,  classified  in  accordance  with  the  percentage 
of  silica  they  contain.  Aluminous  clays  are  those  of  the  Stourbridge  type,  contain- 
ing about  65  per  cent,  of  silica,  "  siliceous  "  those  containing  from  80  to  92  per 
cent,  of  silica,  whilst  those  containing  upwards  of  92  per  cent,  are  known  as  "  silica  " 
materials.  It  is  the  two  last-named  materials  which  are  assuming  great  impor- 
tance in  present-day  gasworks  practice.  Typical  highly  siliceous  clays  are  the  Dinas, 
Ewell,  Ganister,  and  some  Scotch  varieties,  the  best  known  of  the  last  mentioned 
being  the  Bonnybridge  type.  Analyses  of  the  various  materials  as  now  used  on 
gasworks  are  given  below.  To  avoid  confusion,  the  low  silica  clays,  containing  less 
than  72  per  cent,  of  silica,  and  generally  distinguished  by  the  name  fireclays, 
liave  been  referred  to — probably  not  strictly  accurately — as  "  aluminous  "  clays. 


(See  also  under  "  Scotch  Clays.") 


1.  ALUMINOUS  CLAYS. 
Stourbridge  Type. 
Silica 
Alumina 
Ferric  oxide 
Lime 
Magnesia 
Moisture 


2.  SILICEOUS  CLAYS. 

(a)  Oanister.     Oughtibridge  (Type  A). 

Silica     ... 

Alumina 

Titanic  oxide         ... 

Ferric  oxide   .         .          . 

Magnesia        .          . 

Lime      .          .          . 

Potash  .          .          .        .  .          . 

Soda      .         -...          » 

(b)  Ewell  Type. 

Silica     .          .          .         •.          . 

Alumina         *- 

Ferric  oxide  .          .          ..         . 

Lime 

Magnesia        »          .          •       ,   • 

Potash  .        , .          .          .  • ... , 

Soda      .     .'.',.         •  •.:'•• 

Water  of  combination     . 

3.  SILICA  CLAYS. 

(a)  Dinas. 

Silica     .  .  " ,  . 

Alumina     .  .  .  . 

Ferric  oxide  .  .  • . .         . 

Lime     .  .  .  ... 

Potash  ..... 

Soda 


64-62  per  cent. 
21-65 

1-48 

1-88 

0-62 

9-62 
(Bywater.) 


90-2  per  cent. 
7-06 
0-36 
1-03 
0-05 
0-40 
0-56 
0-30 

87-57  per  cent. 
3-60 
4-80 
0-74 
0-41 
0-69 
0-10 
2-09 


97-6     per  cent. 
0-5 
1-5 
0-2 
0-09 
0-03 

(Bywater.) 


134  MODERN   GASWORKS   PRACTICE 

(6)  Black  Ganister. 

Silica     .          .      ,    .         .    '     .          -          •          •  .  .     98-5     per  cent. 

Alumina         .-.-.•         .          .          .          .  .  .       0-3             ,, 

Ferric. oxide             ,          .          .          .          .          .  .  .1-3             ,, 

Lime      .       ••'..          . .0-2 

Potash  .                 • .                            .         .         .  -  .       Traces. 

Soda      .          . "    •     »         ...          .         .  .  Traces. 

(c)  Oughtibridge  (Type  B). 

Silica     .         .         .          .          .         ."   v  '  .         .  -  .     94-78    per  cent. 

Titanic  oxide          .          .          .          .„        .  ,  0-20           „ 

Alumina         .          .          .        '.          .          .          .  .  .       1-65           „ 

Ferric  oxide  .          ...          .          . .        .          .  .  .       0-62           ,, 

Lime      .          ...         .          .  '       .     -    .  .  .       1-51           „ 

Magnesia        .          .         .        .....          .  .  .       0-01           „ 

Potash  .        '.        -.    '      .         ..'         .   . "'- '.    .     ,  .  .       0-54 

Soda      ....  .  0-34 

This  material  is  of  very  similar  nature  to  the  Oughtibridge  type  given  under 
siliceous  clays,  with  the  exception  that  this  variety  is  manufactured  with  the  lime 
bond,  whereas  that  previously  mentioned  is  not. 

(d)  Bonnybridge  (Type  A). 

Silica     .          .          .          .          .         ...          .    '  .  .     95-03  per  cent. 

Alumina         .-..,.         ,         .         .         .  .  .       2-73          ,, 

Ferric  oxide  .                    .         .          .          .          .  .  .       0-45           „ 

Lime     .         .         .         .  .    '  .         .  .  1-80 

Magnesia        .         .         „    .     .         .         .         ,  -  0-11           „ 

4.  SCOTCH  CLAYS  (Aluminous). 
(a)  Glenboig. 

Silica     .          .         ,          .         ,          .       ...  .  .     53-26  percent. 

Alumina         ;         .          .         '.          .          .          .  t  .  42-10 

Ferric  oxide  .         ,          .          .          .          .          .  ^  .  ,   2-08           „ 

Titanic  oxide         V         .          .         '.        -i  .  1-50           „ 

Lime      .          .          .         ...        .          ,  .  .       Trace. 

Magnesia        .          .          .          .          .  -        ...  ,-.  •       Trace. 

Sulphates       ,         »•       ,         ...         .         .  .  •       1-06  per  cent. 

This  analysis  is  somewhat  flattering,  and  the  iron  content  will  frequently  be 
higher. 

(6)  Bonnybridge  (Type  B). 

Silica     .          .          ...          .          .          .  .  .     61-10  per  cent. 

Alumina         .  .       .         .'         .         .         *         .  .  33-64          „ 

Ferric  oxide  ...          .          .       .--••,  -.  2-40           „ 

Lime     ....  .  0-72 

Titanic  oxide.         ». .'      .          .          .          .         .  .  0-89 

Magnesia        .........  0-80          ,, 

Alkalis  .  .  .       0-45 


REFRACTORY  MATERIALS 


135 


Electrode 


Electrode 


THE    TESTING  OF   REFRACTORY  MATERIALS 

In  addition  to  the  ordinary  laboratory  tests  for  the  determination  of  ultimate 
analysis,  refractory  materials  should  be  subjected  to  certain  practical  tests  in  order 
to  determine  their  suitability  for  retort-bench  purposes.  The  tests  usually  applied, 
and  specified  by  the  Refractory  Materials  Committee  of  the  Institution  of  Gas 
Engineers,  are  as  follows : — 

(a)  For  refractoriness. 
(6)  Apparent  porosity. 

(c)  Contraction  or  expansion. 

(d)  Crushing  strength. 

It  must  be  mentioned  at  the  outset  that  refractoriness  is  not  merely  dependent 
upon  the  maximum  temperature  which  the  material  is  capable  of  withstanding 
before  fusion  takes  place.  The  rate  of  change  of 
temperature  has  also  some  considerable  influence, 
and  for  this  reason  it  is  specified  that  for  tests  for 
refractoriness  the  temperature  of  the  experimental 
furnace  shall  be  increased  at  the  rate  of  50°C.  (122° 
Fahr.)  during  five  minutes.  There  are  various  fur- 
naces suitable  for  the  purpose,  but  the  electrical 
apparatus  of  Hirsch,  or  the  Meker  air-gas  type,  are 
to  be  preferred. 

The  Hirsch  furnace  (Fig.  74)  is  of  the  resistance 
type,  the  resistance  material  used  being  chiefly  car- 
bon. The  current  is  led  into  the  furnace  by  means 
of  the  two  electrodes  shown,  these  being  of  iron 
and  embedded  in  a  large  area  of  carbon,  which 
tends  to  keep  them  cool.  The  volume  of  carbon  in 
the  centre  of  the  furnace  is  made  smaller,  so  that  the 

heat  is  concentrated  here.  To  attain  the  maximum  temperature  the  furnace 
requires  a  current  of  130  amperes  at  70  to  80  volts.  The  clay  to  be  tested  is 
mounted  on  the  top  of  the  cylindrical  support  and  introduced  into  the  centre 
tube  of  the  furnace,  this  tube  having  an  internal  diameter  of  2£  inches.  The 
appearance  of  the  sample  undergoing  test  can  be  watched  by  looking  down  the 
centre  tube  from  the  top.  A  weak  current  of  air  constantly  passes  through  the 
centre  tube,  the  object  of  this  being  to  overcome  the  reducing  atmosphere  always, 
associated  with-  carbon  resistance  furnaces. 

The  Meker  furnace  (Fig.  75)  is  capable  of  giving  a  temperature  up  to  1,850°  C. 
(3,360°  Fahr.).  The  main  feature  of  the  apparatus  is  the  special  type  of  Meker 
burner,  requiring  compressed  air  under  a  pressure  of  from  10  to  30  Ib.  per  square 
inch  ;  whilst,  for  effective  results,  the  gas  pressure  should  not  be  below  If  inches. 
A  crucible  of  special  refractory  material  is  mounted  on  a  support,  and  the  flame; 


FIG.  74. — HIRSCH'S  ELECTRIC 
FURNACE. 


136 


MODERN  GASWORKS  PRACTICE 


from    the    burner,    passing   through   the   base    of    the    support,    surrounds   the 
crucible,  and  is  then  turned  downwards  to  its  outlets. 


FIG.  75. — THE  MERER  AIR-GAS  FURNACE. 


Seger  cones  (Fig.  76),  which  partially  fuse,  or  "  squat,"  at  predetermined  tem- 
peratures, are  found  to  provide  the  most  convenient  means  of  recording  the  approxi- 
mate yielding  points  of  the  samples  under  test.  The  Refractory  Materials  Committee 
state  that  two  or  more  tests  are  generally  required  when  an  unknown  material  is 
being  dealt  with.  "  A  preliminary  trial  is  first  made  with  a  piece  of  the  material 

chipped  into  the  approximate  form  of  a 
cone.  This  should  be  cemented  on  to  the 
refractory  slab  of  the  test  furnace  with  a 
mixture  of  alumina  and  best  china  clay, 
together  with  Seger  cones  28,  30  and  32 
(small  size).  Best  china  clay  fuses  between 
cones  35  and  36  ;  and  all  British  fireclays 
fall  below  this  point.  If  cones  28  and  30 

fall,  the  furnace  should  be  cooled,  and  the 
FIG.  76. — SEGER  CONES.  .       . 

material  under    investigation    examined. 

If  it  exhibits  no  sign  of  fusion,  the  trial  should  be  repeated  with  cones  30,  31  and 
32.  By  this  method  of  approximation  it  is  possible  to  decide  whether  the  piece 
vitrified  between  cones  30  and  31  or  between  cones  31  and  32.  The  cones  should, 
in  all  cases,  be  placed  relative  to  the  sample  so  that  both  are  subjected  to  the  same 
temperature.  It  should  be  noted  that  clays  and  related  materials  have  no  sharply 
defined  melting  points,  and  the  definition  of  refractoriness  adopted  refers  to  the 
temperature  at  which  the  angular  edges  of  the  material  begin  to  lose  their  angularity 
when  heated  under  the  conditions  stated." 


REFRACTORY  MATERIALS 


137 


SOFTENING  POINTS  OF  SEGER  CONES. 


Cone  No. 

Cent. 

Fahr. 

Cone  No. 

Cent. 

Fahr. 

022 

600 

1112 

9 

1280 

2336 

021 

650 

1202 

10 

1300 

2372 

020 

670 

1238 

11 

1320 

2408 

019 

690 

1274 

12 

1350        2462 

018 

710 

1310 

13 

1380        2516 

017 

730 

1346 

14 

1410        2570 

016 

750 

1382 

15 

1435        2615 

015a 

790 

1454 

16 

1460        2660 

014a 

815 

1499 

17 

1480        2696 

013a 

835 

1535 

18 

1500        2732 

012a 

855 

1571 

19 

1520        2768 

Olla 

880 

1616 

20 

1530        2786 

OlOa 

900 

1652 

26 

1580        2876 

09a 

920 

1688 

27 

1610        2930 

08a 

940 

1724 

28 

1630        2966 

07a 

960 

1760 

29 

1650        3002 

06a 

980 

1796 

30 

1670        3038 

05a 

1000 

1832 

31 

1690        3074 

04a 

1020 

1868 

32 

1710        3110 

03a 

1040 

1904 

33 

1730        3146 

02a 

1060 

1940 

34 

1750        3182 

Ola 

1080 

1976 

35 

1770 

3218 

la 

1100 

2012 

36 

1790 

3254 

2a 

1120 

2048 

37 

1825 

3317 

3a 

1140 

2084 

38 

1850 

3362 

4a 

1160 

2120 

39 

1880 

3416 

5a 

1180 

2156 

40 

1920 

3488 

6a 

1200        2192 

41 

1960 

3560 

7 

1230        2246 

42 

2000 

3632 

8 

1250 

2282 

— 

TESTING  UNDER  STRESS 

Although  the  conditions  of  testing  in  furnaces  such  as  described  above  coincide 
with  those  prevailing  in  a  retort  setting  in  respect  of  temperature,  it  must  not  be 
forgotten  that  the  fireclay  material  forms  part  of  a  structure,  and  is,  in  consequence, 
subjected  to  varying  degrees  of  stress  (chiefly  compressive)  according  to  its  function 
in  the  setting.  In  this  respect  a  series  of  tests  have  been  carried  out  by  Dr.  J.  W. 
Mellor  l  to  determine  the  effect  of  stress  upon  ultimate  refractoriness.  The  effects 
of  comparatively  light  loading  are  certainly  a  matter  for  surprise,  and  a  decrease 
in  refractoriness  of  from  12  to  13  per  cent,  has  resulted  from  loading  equivalent 
to  54  Ib.  per  square  inch. 


Report  of  Refractory  Materials  Committee,  1914. 


138 


MODERN   GASWORKS   PRACTICE 


APPARENT  POROSITY 

The  test  for  apparent  porosity  really  indicates  the  density  of  the  material, 
and  gives  the  percentage  of  the  total  volume  which  is  occupied  by  air  spaces. 

Volume  of  air  spaces 

Percentage  porosity  =  >-,  ,  , ; —     —7—      — : x  100. 

Total  volume  of  test  piece 

Porosity  is  one  of  the  most  important  properties  of  present-day  fireclay  articles, 
and  is  determined"  by  means  of  some  forms  of  "  voluminometer  "  or  "  porosometer," 
as  shown  in  Fig.  77.  The  piece  to  be  tested  should  be  of  the  size  of  half  a  brick, 

having  a  volume  of  about  700  c.c.  The 
principle  of  the  test  is  based  on  the  absorp- 
tion by  the  brick  of  a  suitable  liquid 
(usually  paraffin)  until  the  air  spaces  and 
cavities  are  completely  filled.  The  volume 
of  liquid  required  for  this  purpose  can  be 
measured  in  the  burette,  this  being  iden- 
tical with  the  volume  of  the  air  spaces, 
hence  the  porosity  may  be  determined. 
The  test  piece,  dried  at  100°  C.,  is  placed 
in  the  glass  jar ;  the  paraffin  from  the 
latter  having  been  previously  sucked  up 
into  the  burette  by  means  of  a  water 
pump.  Another  water  pump  is  then 
connected  to  the  lid  of  the  jar  contain- 
ing the  test  piece,  and  as  much  air  as 
possible  is  sucked  out.  With  the  pump 
still  working,  the  paraffin  is  then  allowed 
to  enter  the  jar  slowly  until  the  brick  is 
completely  covered,  the  pump  sucking 
away  the  air  from  the  interstices  of  the 
brick,  paraffin  taking  its  place.  By 
levelling  and  reading  the  burette,  the 
volume  of  liquid  displaced  by  the  solid 
portion  of  the  test  piece  will  be  given. 
The  volume  of  the  soaked  brick  is  then 
found  by  displacement  in  a  similar  man-, 

ner,  thus  giving  the  total  volume  of  the  test  piece,  and  the  percentage  porosity 
calculated  as  above. 


FIG.  77. — MELLOR'S  POROSOMETER. 


LINEAR   CONTRACTION  OR  EXPANSION 

By  this  is  meant  the  percentage  change  in  length  which  occurs  when  the  test 
piece  is  heated  under  stated  conditions.  "  A  carborundum  wheel  may  be  used  for 
grinding  the  ends  of  the  test  pieces  flat,  and  one  of  the  Meker  furnaces  may  be  em- 
ployed for  carrying  out  the  test.  The  test  piece  should  be  supported  horizontally, 


REFRACTORY   MATERIALS  139 

and  fired  along  with  cones  13,  14  and  15.  As  soon  as  cone  14  has  squatted,  it  ceases 
to  furnish  any  further  indication  of  the  temperature  of  the  muffle ;  so  that  the 
subject  temperatures  should  be  ascertained  at  about  15-minute  intervals,  by 
means  of  a  pyrometer.  It  is  essential,  however,  that  the  temperature  should  remain 
constant ;  and  if  it  is  necessary  to  remove  plugs,  etc.,  for  the  purpose  of  obtaining 
the  temperature,  great  care  must  be  taken  to  avoid  cooling  the  furnace  by  such 
means.  As  in  the  test  for  refractoriness,  the  cones  should  be  placed  in  such  a  position 
relative  to  the  sample  under  test  that  both  may  be  subjected  to  the  same  tempera- 
ture." 

The  Refractory  Materials  Committee  specify  the  following  limits  for  various 
materials  so  far  as  contraction  or  expansion  is  concerned  : — 

Retort  Material. — A  test  piece  heated  to  a  temperature  of  cone  14  (2y570°  Fahr.) 
for  two  hours  shall  not  show,  when  cold,  more  than  1J  per  cent,  contraction  or 
expansion.  The  test  piece  is  to  be  4£  inches  long  by  4|  inches  wide,,  with  the  ends 
ground  flat.  Readings  as  to  length  are  to  be  taken  by  means  of  Vernier  callipers 
reading  to  0-1  mm. 

Firebricks,  Blocks,  and  Tiles. — A  test  piece  when  heated  under  the  above  con- 
ditions shall  not  show  more  than  1  per  cent,  or  1 J  per  cent,  contraction  or  expansion, 
according  to  the  grade  of  material. 

Silica  Articles. — A  test- piece  when  heated  for  two  hours  to  a  temperature  of 
cone  12  (2,462°  Fahr.)  shall  not  show,  when  cold,  more  than  0-75  per  cent,  linear 
contraction  or  expansion. 

CRUSHING   STRENGTH 

The  compressive  strength  of  fireclay  articles  may  be  determined  by  means 
of  one  of  the  forms  of  apparatus  made  for  the  testing  of  materials.  With  regard 
to  ordinary  Stourbridge  articles,  these  should  be  capable  of  withstanding  a  crushing 
stress  of  not  less  than  1,800  Ib.  per  square  inch. 

THE    RELATION   OF   REFRACTORY   MATERIALS    TO    THE    VARIOUS 
PORTIONS  OF  A  RETORT  SETTING 

In  dealing  with  fireclay  articles  and  their  relation  to  the  various  portions  of  a 
retort  bench,  it  is  proposed  to  consider  the  matter  from  the  purely  practical  stand- 
point of  the  gas  engineer,  and  to  avoid,  so  far  as  possible,  the  inclusion  of  abstruse 
technical  details,  which  are  of  chief  concern  to  the  scientist  and  investigator.  Such 
prominence  is  given  nowadays  to  the  question  of  refractory  materials  that  every 
gasworks  official  is  more  or  less  an  authority  on  the  subject.  It  must  be  admitted, 
however,  that  it  is  chiefly  the  technical  manufacture  of  the  articles  around  which 
argument  is  waged,  whereas  the  everyday  facts  concerning  the  suitability  of  various 
materials  for  some  particular  function  receive  but  a  meagre  share  of  attention. 
Errors  of  judgment  in  the  selection  of  fireclays  are  only  too  common,  even  in  the 
present  semi- enlightened  age  ;  and,  undoubtedly,  considerable  trouble  and  expense 
'could  be  avoided  if,  in  the  first  place,  the  purchaser  studied  his  requirements  on 
-methodical  lines.  To  this  end,  it  is  suggested  that  the  conditions  which  any  particular 


140  MODERN   GASWORKS   PRACTICE 

material  may  be  called  upon  to  withstand  should  be  subjected  to  a  preliminary 
investigation  on  lines  such  as  the  following : — 

1.  Is  the  temperature  high  or  moderate  ?     "  Moderate  "  may  be  considered 
up  to  1,850°  Fahr.     "  High,"  up  to  2,800°  Fahr.     As  a  matter  of  fact,  the  latter 
temperature  should  seldom  be  necessary  in  the  m'odern  combustion  chamber ;   the 
figure  being  usually  in  the  neighbourhood  of  2,500°  Fahr. 

2.  Will  there  be  fluctuations  of  temperature  ?     This  is  one  of  the  most  trying 
•conditions  which  the  material  can  be  called  upon  to  withstand.     If  the  setting  is 
•worked  correctly  there  should  be  nothing  in  the  way  of  violent  fluctuations,  except, 
perhaps,  in  the  retorts.     It  must  be  remembered  that  there  may  be  so  great  a  fall 
in  temperature  as  1,000°  Fahr.  when  a  retort  is  freshly  charged. 

3.  Will  the  material  come  into  direct  contact  with  the  flame,  or  will  there  be 
.a  "  cutting  heat  "  ?     By  a  "  cutting  heat "  is  usually  understood  a  fierce,  localized 
flame,  the  effect  of  which  is  exaggerated  by  the  presence  of  flue  dust  in  the  gases. 
This  dust  may  contain  upwards  of  50  per  cent,  of  injurious  iron  compounds. 

4.  Is  mechanical  strength  required  ?     Various  portions  of  the  retort  bench 
take  their  place  in  ensuring  the  stability  of  the  structure  ;    hence,  in  addition  to 
withstanding  high  temperatures,  they  are  called  upon  to  withstand  working  stresses. 

5.  Is  heat  to  be  conducted  or  retained  ?     This  is  a  point  which  arises  chiefly 
when  deciding  upon  material  for  regenerators  and  the  external  walls  of  settings. 
In  order  to  prove  a  good  conductor  of  heat,  the  material  must  be  dense,  and  manu- 
factured with  as  close  a  grain  as  possible.     On  the  other  hand,  for  the  retention  of 
teat  the  texture  must  be  as  open  as  possible  ;  which  accounts  for  the  extreme 
lightness  of  many  of  the  insulating  bricks  (such  as  "  Thermalite  ")  now  to  be  obtained. 

6.  Is  the  material  likely  to  be  affected  by  external  fluxes  ?     The  small  per- 
centage of  low-fusing  constituents  present  in  the  fireclay  is  more  or  less  harmless 
when  left  to  itself  ;  but  if  incipient  "  slagging  "  is  set  up  by  other  fusible  substances 
introduced  from  outside,  there  is  no  telling  where  the  trouble  may  end.     Iron  dust 
in  the  producer  gases   and  clinker  adhering  to  the  sides  of  the  furnace  walls   are 
the  chief  offenders  in  this  direction. 

7.  Will  the  material  be  subjected  to  an  oxidizing  or  to  a  reducing  atmosphere  ?  A 
reducing  atmosphere  (i.e.,  an  atmosphere  of  carbon  monoxide)  is  more  trying  than 
oxidizing  conditions ;    but  if   a  retort  bench  is  being  correctly  operated,  the  only 
possible  point  at  which  a  reducing  atmosphere  could  continuously  prevail  would 
be  above  the  fuel  in  the  furnace  and  below  the  nostril  arch.     If  carbonic  oxide  is 
found  at  a  point  beyond  this,  it  is  certainly  indicative  of  a  shortage  of  secondary 
air.     The  Relractory  Materials  Committee  are  evidently  satisfied  that  the  reducing 
atmosphere  test  is  not  of  sufficient  importance  to  warrant  the  use  of  the  compara- 
tively complicated   apparatus  which  it  entails,  for  in  their   specification  of  retort 
jnaterial  a  test  atmosphere  of  an  oxidizing  nature  is  specified. 

THE  RETORTS. 

It  is  not  within  the  power  of  the  retort  manufacturers  to  alter  materially  the 
'chemical  composition  of  the  clay  occurring  in  their  districts ;  hence  it  is  by  modifi- 


REFRACTORY  MATERIALS  141 

cation  of  the  texture  of  the  finished  article  and  attention  to  the  details  of  manu- 
facture that  greatly  increased  refractoriness  has  been  obtained.  Not  only  do 
the  retorts  have  to  withstand  high  heats,  but  in  addition,  as  discharging  and  charging 
takes  place,  they  are  exposed  to  considerable  fluctuations  in  temperature.  More- 
over, they  must  be  of  a  certain  mechanical  or  physical  strength  in  order  to  carry 
the  loads  to  which  they  are  subjected  and  to  resist  the  strains  put  upon  them  by 
modern  stoking  machinery.  In  the  case  of  the  full  coal  charge  and  "  pusher," 
the  retort  has  to  withstand  some  considerable  bursting  pressure  in  the  event  of  a 
charge  jamming-up  and  refusing  to  move.  For  high  temperature,  a  highly  refractory 
material  is  required  ;  and  to  obtain  this,  high  porosity  and  a  fairly  open  grain  are 
essential.  This  is  chiefly  due  to  the  fact  that  an  open  grain  means  larger  individual 
particles,  and  the  heat  and  flame  have  greater  difficulty  in  penetrating  to  the  interior 
of  these  than  in  the  case  of  smaller  dust-like  particles.  The  main  function  of  porosity, 
however,  is  that  of  imparting  to  the  material  the  ability  to  withstand  fluctuation 
in  temperature.  For  mechanical  strength,  on  the  other  hand,  a  close-grained  material 
of  high  density  gives  the  best  results,  whilst  diffusion  of  coal  gas  outwards  or  furnace 
gas  inwards  through  the  walls  of  the  retorts  is  more  effectively  restricted,  and  better 
thermal  conductivity  is  obtained.  In  the  manufacture  of  the  retort,  therefore, 
these  contrary  requirements  have  to  be  reconciled  as  far  as  possible,  although  greater 
attention  is  usually  paid  to  refractoriness.  It  is  in  this  way  that  porosity  plays 
so  important  a  part ;  and  no  doubt  the  success  of  the  German-made  retort  (which 
even  now  has  a  higher  porosity  than  the  specified  English  type)  can,  in  all  probability, 
be  greatly  attributed  to  this  fact.  Porosity,  however,  as  will  be  realized,  is  a  some- 
what dangerous  property  to  interfere  with,  unless  considerable  care  is  exercised 
to  keep  it  within  the  prescribed  limits.  It  cannot  be  denied  that  any  increase  in 
porosity  may  be  accompanied  by  a  corresponding  decrease  in  the  capacity  of  the 
material  to  withstand  working  stresses ;  hence  too  much  zeal  in  the  open-grain 
doctrine  is  likely  to  tell  somewhat  seriously  when  the  working  life  of  a  retort  comes 
to  be  reckoned  up.  Evidence  of  this  is  seen  in  a  certain  number  of  retorts  having 
a  porosity  up  to  as  much  as  30  per  cent,  which  at  one  time  found  their  way  into 
gasworks  with  decidedly  unhappy  results.  In  this  connexion  it  is  particularly 
interesting  to  note  that,  whilst  the  Refractory  Materials  Committee  specify  a  mini- 
mum porosity  of  18  per  cent.,  the  German-made  retort  has  an  average  in  the  neigh- 
bourhood of  25  per  cent.  It  has  been  shown,  too,  that  in  this  country  the  German 
retorts,  with  due  care,  are  capable  of  surviving  about  2,100  days.  A  comparison 
between  working  life  and  porosity  in  this  way  is  striking,  in  that  it  shows  that  even 
with  a  comparatively  open  texture  a  high  degree  of  mechanical  strength  is  obtain- 
able. A  rather  puzzling  fact,  however,  is  that,  judging  from  appearance,  the  German 
material  gives  an  impression  of  lower  porosity  than  the  English  specification  type. 
(See  Figs.  78  and  79.)  The  open  grain  shown  in  Fig.  78  gives  a  very  good  indica- 
tion of  the  manner  in  which  increased  refractoriness  over  the  original  material 
(Fig.  80)  has  been  obtained.  With  regard  to  conductivity,  it  has  been  shown  that  if 
an  ordinary  fireclay  retort  is  burnt  at  1,900°  Fahr.,  and  the  final  substance  is  taken 
as  giving  a  standard  coefficient  of  conductivity  (i.e.,  1),  the  figure  will  be  in- 


142 


MODERN   GASWORKS   PRACTICE 


creased  to  1  -6  if  burning  takes  place  at  2,350°  Fahr.     It  is  for  this  reason  that  a 
retort  will  give  a  greater  conductivity  after  having  been  in  use  for  some  time. 

The  practice  of  coating  the  inner  surfaces  of  the  retort  with  a  glaze,  which  is 
prevalent  in  Germany,  has  never  gained  much  favour  here,  although  in  the 
Williamson-Cliff  new  type  of  retort  this  is  done.  The  glaze  is  primarily  intended 
to  act  as  an  impervious  coating  to  prevent  diffusion  of  gas  through  the  retort  walls. 
The  friction  of  the  stoking  machinery  disposes  of  the  greater  part  of  it ;  but  by 
this  time  "  scurf  "  will  have  formed,  and  will  take  up  the  duty  of  the  glaze.  Experi- 
ments have  recently  been  conducted  in  connexion  with  the  problem  of  the  Outward 


FIG.  78. — SECTION  OF  STANDARD  SPECIFI- 
CATION MATERIAL. 


FIG.  79. — SECTION  OF  TYPICAL  GERMAN 
RETORT  MATERIAL. 


diffusion  of  gas  through  the  retort  walls  during  the  early  stages  of  the  charge,  when 
the  retorts  may  be  subjected  to  some  pressure,  and  it  is  a  question  whether  the 
increased  porosity  of  the  material  is  not  an  offender  in  this  direction.  When  perfectly 
new  retorts  are  in  use,  there  is  little  doubt  that  some  gas  must  be  lost  in  this  way, 
although  the  formation  of  "  scurf  " — a  fairly  speedy  operation — will  soon  act  as 
a  check.  The  effect  of  carbon  in  sealing  up  the  interstices  of  the  retort  walls  is 
well  illustrated  by  the  photograph  shown  in  Fig.  84.  When  demolishing  old  retort 
benches,  it  is  very  usual  to  find  a  black  stripe  running  completely  round  the  section 
of  the  retort.  The  stripe,  commencing  about  a  quarter  of  an  inch  from  the  inner 
surface  of  the  material,  will  usually  run  to  about  an  inch  in  width,  and  is  plainly 


FIG.  80. — SECTION  OF  ORIGINAL  RETORT. 
MATERIAL. 


FIG.  81. — EXTERIOR  SURFACE  OF  ORIGINAL 
MATERIAL. 


fig 


FIG.  82. — EXTERIOR  SURFACE  OF  SPECIFI-  FIG.    83. — INTERIOR   SURFACE    OF   RETORT 

CATION  MATERIAL.  AFTER  500  WORKING  DAYS. 

143 


144 


MODERN   GASWORKS   PRACTICE 


seen  in  Fig.  84.  It  is  somewhat  puzzling  to  know  why  this  "  carbonized  "  layer 
should  be  sandwiched  in  the  material  in  this  way.  The  explanation  would  appear 
to  be  that  the  inner  deposits  are  burned  out  with  the  inrush  of  air  as  the  retort 
doors  are  opened  for  charging  or  "  scurfing."  An  analysis  of  the  black  layer  has- 
shown  that,  on  an  average,  it  contains  10  per  cent,  of  free  carbon. 

Retorts  in  this  country  are  made  by  two  distinct  methods,  i.e.,  hand-moulding 
and  machine-pressed.  The  former  method  is  still  employed  in  many  yards  to-day, 
and  consists  in  plastering  the  clay  to  a  certain  thickness  round  a  "  plug  "  of  the 

required  shape.  The  whole  length  of 
the  retort  is  not  plastered  on  in  one 
operation,  but  is  formed  in  stages  of 
about  18  inches  to  2  feet  in  length  at  a 
time.  The  mandril  is  placed  in  a  verti- 
cal position,  and  after  the  first  stage 
has  been  moulded  it  is  permitted  to 
stand  aside  for  a  day  or  two  until 
sufficiently  dry  to  bear  the  weight  of 
the  next  stage.  In  some  instances,, 
chiefly  on  the  Continent,  a  different 
method  is  used.  An  outer  casing  is 
fitted  with  a  core  so  as  to  form  an 
annular  space  corresponding  to  the 
shape  of  the  retort.  The  clay  substance 
is  then  rammed  into  the  space  by  means 
of  long- handled  punners  provided  with 
spiked  ends.  The  object  of  the  spikes 
is  to  release  air  bubbles  which  would 
affect  the  porosity  of  the  finished  article. 
Machine  presses  for  retort  making 
(Fig.  85)  are  chiefly  operated  by  steam 
power,  and  consist  of  a  large  cast-iron 
cylinder  in  which  the  piston  or  "  press- 
head  "  works.  The  cylinder  is  filled  up  with  a  certain  quantity  of  clay,  depending 
upon  the  capacity  of  the  machine,  and  as  the  piston  goes  down  the  clay  is  com- 
pressed and  forced  through  a  die  at  the  base  of  the  cylinder.  The  die  is  fashioned 
in  accordance  with  the  shape  of  the  retort  required,  and  as  the  moulded  clay  passes 
through,  it  is  supported  by  a  movable  table,  which  descends  at  the  same  rate  as. 
the  compressing  cylinder.  The  moulded  retort  issuing  from  the  die  and  resting 
on  the  movable  table  is  shown  in  Fig.  86.  Machines  of  this  description  are; 
capable  of  making  400  to  500  feet  of  retort  per  day. 

THE  QUALITIES  or  HAND-MADE  AND  MACHINE-PRESSED  RETORTS 
With  regard  to  manufacturing  costs,  there  is  little  to  choose  between  the  two 
types  of  retort,  but  from  the  point  of  view  of  working  life  the  hand-made  article 


FIG.  84. — SECTION  OF  USED  RETORT  SHOWING 
CARBON  LAYER. 


REFRACTORY   MATERIALS 


145 


is  usually  to  be  preferred.  The  fact  that  the  machine  type  is  made  in  a  single 
operation  may  account  for  somewhat  greater  homogeneity,  but  the  gradual  building 
up  in  distinct  lifts  ensures  slower  drying,  which  is  desirable.  Machine-made  retorts 
are  denser  and  heavier,  but  an  excess  of  density  can  be  avoided  by  the  addition 
of  sawdust  or  coarser  grogram.  Owing  to  the  high  working  pressure  of  the  machines 
the  prepared  clay  must  of  necessity  be  stiff,  otherwise  warping  and  sagging  will 
occur  after  the  material  has  passed  the  die.  Stiff  material  put  together  by  pressure 


FIG.  85. — A  STEAM-DRIVEN  RETORT-MOULDING  MACHINE, 
SHOWING  LOWER  PORTION  OF  STEAM  CYLINDER  AND 
UPPER  PART  OF  CLAY  CYLINDER,  THE  LATTER  WITH 
PISTON  UP  so  THAT  IT  MAY  BE  CHARGED  WITH  CLAY. 


FIG.    86. — RETORT    PASSING 
THROUGH  MOULDING  DIE. 


is  not  so  effective  for  most  purposes — particularly  retort  work — as  a  more  plastic 
clay  which  is  put  together  by  hand.  When  the  clay  is  plastic,  the  additional  amount 
of  water  is  afforded  an  opportunity  of  carrying  out  its  function  of  knitting  and 
binding  up  the  particles.  Moreover,  when  the  ram  under  heavy  pressure  squeezes 
or  drives  the  clay  out  of  a  retort  machine,  there  is  a  tendency  to  destroy  the  best 
setting  of  the  grog  and  to  drive  the  coarse  particle  into  a  more  or  less  regular  forma- 
tion. On  the  other  hand,  the  machine-made  retort,  prepared  with  due  care,  is  far 
cleaner,  more  regular  and  straighter  than  that  made  in  successive  lifts  by  hand. 

SEGMENTAL  RETORTS 

From  the  point  of  view  of  working  life,  segmental  or  built-up  retorts  are  far 
superior  to  the  common  moulded  type,  but,  chiefly  owing  to  the  preliminary  expense 


146  MODERN   GASWORKS   PRACTICE 

incurred,  they  have  not  been  very  generally  adopted  in  this  country.  Built-up 
retorts  may  be  classified-  under  two  headings,  namely,  those  composed  of  large 
segments  and  those  constructed  from  special  small  blocks  about  the  size  of  an 
ordinary  brick.  It  has  been  said  that  retorts  built  up  from  small  tongued  and 
grooved  segments  can  be  worked  continuously  for  five  years  without  requiring 
repairs,  the  explanation  being  that  the  flexible  units  give  and  take  with  the  expansion 
and  contraction  caused  by  the  variation  of  temperature  in  the  setting.  In  the 
case  of  a  brick  retort,  the  line  of  fracture  necessarily  follows  along  the  joint-lines, 
whereas  in  the  case  of  a  moulded  retort  the  line  of  cleavage  is  indefinite,  and  cross- 
stresses  are  set  up.  Under  local  heating,  it  is  impossible  to  expect  perfectly  uniform 
movement ;  thus,  when  the  retort  is  composed  of  one  single  piece,  cracks  and  fissures 
result.  In  these  days  of  the  "  pusher,"  moreover,  distortion  must  be  avoided  if 
the  charge  is  not  to  jam  up.  In  this  respect,  the  built-up  retorts  composed  of  small 
units  are  probably  to  be  preferred  to  those  in  which  large  sections  are  employed, 
although  opinion  in  this  respect  differs  considerably. 

The  retort  built  up  of  small  units  is  extremely  flexible,  and  yet  (owing  to  the 
tongued  and  grooved  joint)  little  or  no  leakage  takes  place.  A  difficulty,  however, 
arises  when  "  scurfing "  is  considered,  for,  owing  to  their  delicate  adjustment, 
the  separate  units  are  liable  to  be  damaged  with  the  heavy  tool  employed  and  the 
rough  handling  they  receive.  Furthermore,  there  is  the  possibility  of  the  carbon 
getting  into  the  joints  and  opening  out  the  bricks  in  this  way.  Segmental  retorts 
require,  of  course,  substantial  and  at  the  same  time  flexible  supports,  this  being 
another  factor  which  adds  to  the  expense.  With  regard  to  the  relative  "  gas-tight- 
ness "  of  the  two  types  of  retort,  there  appears  to  be  some  divergence  of  opinions. 
It  may  be  generally  taken,  however,  that,  so  long  as  the  segments  are  carefully 
made  and  laid  together,  the  gas  leakage  will,  in  the  long  run,  be  less  than  with  the 
moulded  retort,  in  spite  of  the  number  of  joints  necessitated.  Some  authorities 
attribute  the  tightness  of  the  segmental  retort  to  the  fact  that  when  a  line  of 
cleavage  occurs,  it  runs  along  the  joints  and  is  quickly  sealed  by  the  formation  of 
scurf.  With  the  moulded  retort,  on  the  other  hand,  the  cracks  may  be  anything 
from  £  inch  to  1  inch,  or  even  greater.  The  built-up  retort,  moreover,  lends 

itself  to  effective  repair.  Bywater  has 
stated  that  for  horizontal  retorts  the 
use  of  the  segmental  principle,  although 
heavier  in  initial  cost,  results  in  a  saving 
of  more  than  Id.  per  ton  of  coal  car- 
bonized during  their  life. 

A  typical  brick-built  retort  with 
tiled  bottom,  of  a  somewhat  old- 
fashioned  type,  is  shown  in  Fig.  87, 
whilst  the  more  common  forms  of  seg- 
mented retorts  are  illustrated  in  Fig. 

I  88.     In  all  cases  where  the  latter  types 

87.— BRICK  RETORT  WITH  TILED  BASE.      are    used    the    modern    tendency    is   to 


REFRACTORY   MATERIALS 


147 


employ  a  highly  refractory 
material  of  a  silica  nature 
(such  as  the  Oughtibridge  or 
Bonnybridge  types)  ;  but  ex- 
perience has  shown  that  this 
clay  is  of  little  avail  in  with- 
standing the  erosion  caused  by 
friction  of  the  coke.  Accord- 
ingly, while  the  arch  of  the 
retort  is  composed  of  silica 
material,  the  shoulders  and 
base  are  made  from  an  alumin- 
ous clay  of  a  Stourbridge 
nature,  as  shown  in  Fig.  89. 
With  occasional  repairs,  re- 
torts of  this  description  have, 
in  some  instances,  recorded  a 
working  life  of  3,000  days. 
Some  idea  of  the  longevity  of 
the  segmental  chamber  retort 
may  be  gathered  from  the  fact 
that  the  ovens  employed  in 
the  Munich  chamber  instal- 
lations have,  in  many  cases, 
been  in  use  for  nine  consecu-  FlG.  88.— TYPES  OF  BUILT-UP  RETORTS. 

tive  years. 

To  overcome  the  inability  of   the   silica  ware  to  withstand   friction,  A.  ClifT 
has  suggested  the  adoption  of  a  composite  retort  as  shown  in  Fig.  90. 


FIG.     89. — SEGMENTAL     RETORT     WITH 
SILICA  ARCH  AND  ALUMINOUS  BASE. 


FIG.  90. — COMPOSITE  RETORT  WITH  ALUMINOUS 
BOTTOM. 


In  some  instances  the  segments  composing  a  rebated  retort  are  carried  right  up 
to  both  ends,  and  cast-iron  sheaths  (similar  to  that  shown  in  Fig.  102,  p.  157)  are 


148 


MODERN  GASWORKS   PRACTICE 


used  for  attaching  the 
mouthpiece.  The  more 
modern  and  satisfactory 
method,  however,  is  to 
form  the  last  couple  of 
feet  from  a  short  length 
of  moulded  retort  as 
FIG.  91. — SEGMENTAL  RETORT  WITH  MOULDED  MOUTHPIECES.  seen  in  Fig.  91.  This 

is,  as  in  the  ordinary  way, 

composed  of  Stourbridge  clay,  which  possesses  the  advantage  that  it  is  not  injured 
by  the  condensed  alkaline  vapour  falling  back  from  the  ascension  pipe.  Silica 
material,  on  the  other  hand,  is  quickly  reduced  to  a  powder  in  this  way. 

THE  CORROSION  OF  EETORTS 

A  contingency  of  no  little  concern  to  the  coke-oven  engineer,  but  fortunately 
occasioning  but  small  anxiety  in  connexion  with  gasworks'  retorts,  is  the  damage 
caused  to  fireclay  by  saline  corrosion.  All  coals  contain  a  certain  amount  of  sodium 
chloride,  and  apparently  when  this  is  decomposed  the  basic  salt  of  sodium 
combines  with  the  surface  of  the  retorts  or  bricks,  thus  forming  an  injurious  coating 
on  the  interior.  This  coating,  being  sensitive  to  the  variations  of  temperature, 
cracks  and  opens,  so  that  further  quantities  of  the  harmful  fumes  can  enter,  and 
in  time  the  retort  becomes  covered  with  a  crumbling  substance  of  low-fusing  point. 
In  the  affected  portions  the  proportion  of  silica  may  be  reduced  by  so  much  as 
6  per  cent.,  while  the  injurious  alkaline  impurities  are  increased  by  over  3  per  cent., 
this  greatly  aggravating  the  tendency  of  the  material  to  "  run."  Fortunately, 
the  majority  of  gas  coals  in  general  use  contain  only  small  quantities  of  sodium 
chloride,  and  thus  the  effect  is  not  particularly  marked.  At  many  coke-oven  plants, 
however,  the  chamber  walls  have  to  be  replaced  in  less  than  twelve  months,  owing 
to  the  action  of  the  salt,  and  this  in  spite  of  the  fact  that  the  coals  are  almost 
without  exception  washed  before  use,  as  there  is  a  certain  proportion  of  the  salt  so 
closely  incorporated  with  the  coal  that  the  ordinary  washing  methods  are  ineffective 
in  removing  it.  Observations  made  at  a  coke-oven  works  showed  that  a  propor- 
tion of  0-143  per  cent,  of  salt  in  the  water  employed  for  washing  coals  ruins  a 
retort  in  three  years,  while  one-quarter  of  this  amount  renders  a  refractory  sub- 
stance of  little  value  after  five  years'  work. 

THE  COST  OF  RETORTS 

At  the  present  time,  prices  for  retorts  must  be  given  with  caution,  as  there 
are  somewhat  obvious  indications  that,  with  the  stipulations  applied  to  manufacture 
and  the  better  quality  of  articles  turned  out,  the  figures  are  unlikely  to  remain 
stationary.  At  the  same  time,  much  depends  upon  the  locality,  also  the  size  of 
the  works,  the  larger  works  with  big  demands  naturally  being  supplied  at  a  lower 
figure  than  a  smaller  concern  requiring  an  identical  article.  Taking  London  delivery 
as  an  average  instance,  however,  the  following  figures  may  be  given  : — 


REFRACTORY   MATERIALS  149 

Standard  specification  retorts.          .  .  5s,  9d.  to  6s.  6rf.  per  foot  run,  delivered. 

Good  quality  (not  to  specification).  .  4s.  8d.  to  5s.  2d.              „                „ 

German  retorts       .          .          .          .  .  7s.  to  8s.                            „                 „ 
Segrnental  retorts : 

1.  All  aluminous  material    .      .  .  6s.  6d.  to  7s.  3d.              „                „ 

2.  Silica  tops,  aluminous  base      .  "  ,'•  7s.  Qd.  to  8s.                     „                 ,, 

These  prices  are  all  for  average  sizes.  The  very  large  patterns  would  be  slightly 
more  costly,  whilst  very  small  sizes  would  be  rather  less.  Special  shapes  are,  of 
course,  extra. 

With  regard  to  the  actual  laying  of  segmental  retorts,  an  additional  cost  (com- 
pared with  moulded  types)  of  from  9d.  to  Is.  per  foot  should  be  allowed. 

SILICA   RETORTS 

Retorts  made  entirely  from  silica  material,  although  little  beyond  the  experi- 
mental stage,  have  been  used  to  some  extent  in  the  gasworks  of  America.  Silica 
material,  per  se,  has  no  binding  properties,  and  the  clay  made  use  of  (containing 
about  95  per  cent,  of  silica)  is  moulded  by  the  introduction  of  about  2  per  cent,  of 
some  binding  substance,  such  as  lime.  The  finished  articles  are  extremely  fragile, 
and  require  great  attention  during  heating-up  if  cracks  and  fissures  are  to  be  avoided. 
Furthermore,  it  seems  that  they  are  not  capable  of  standing  any  considerable  loading 
when  under  heat.  In  all  instances,  with  the  exception  of  concentric  rings  used 
in  vertical  retort  systems,  the  silica  retorts  so  far  made  use  of  have  been  of  the 
segmented  pattern,  although  in  some  cases  a  moulded  aluminous  end  is  used,  as 
previously  described.  Owing  to  the  somewhat  excessive  expansion  of  this  type 
of  material — amounting  to  as  much  as  1J  per  cent,  of  its  original  length — great 
attention  has  to  be  given  to  the  setting  of  the  segments,  and  joints  are  in  some 
cases  made  with  thin  cardboard,  which  eventually  burns  away,  making  room  for 
the  increase  in  length.  Another  compensating  method  is  to  make  moderately  thick 
joints  of  an  aluminous  clay,  which,  on  heating-up,  contracts  and  makes  way  for 
the  expansion  of  the  silica.  According  to  investigations  carried  out  by  the  Refractory 
Materials  Committee  of  the  Institution  of  Gas  Engineers,  the  life  of  silica  retorts, 
when  used  in  conjunction  with  stoking  machinery,  is  from  3|  to  4  years.  One  of 
the  chief  merits  of  the  silica  material  is  its  proclivity,  owing  to  a  much  denser  grain, 
to  transmit  heat  far  more  readily  than  is  the  case  with  articles  made  from  the  ordinary 
mixture  of  aluminous  clay  and  grog.  Owing  to  this  fact  a  certain  saving  of  fuel 
can  be  looked  for,  although  the  chief  advantage  lies  in  the  increased  carbonizing 
capacity  of  the  retorts.  That  is  to  say,  more  coal  is  capable  of  being  dealt  with 
in  a  definite  period  owing  to  the  possibility  of  burning-off  the  charge  much  more 
rapidly.  Silica  material  should  on  no  account  be  exposed  to  the  action  of  the  weather. 

PROTECTION  FOR  RETORTS 

Owing  to  the  expansion  of  the  siliceous  material  employed  in  the  cross-walls 
and  other  portions  of  the  setting,  the  retorts  often  suffer  damage  from  the  increased 
stresses  put  upon  them.  A  method  for  overcoming  this  effect,  which  has  been 


150 


MODERN   GASWORKS   PRACTICE 


FIG.  92. — THE  WOODEN  STRIP  IDEA. 


employed  with  some 
considerable  success,  is 
that  shown  in  Fig.  92. 
The  idea,  as  will  be  seen 
from  the  sketch,  consists 
in  placing  a  shuttering 
of  wooden  strips  com- 
pletely around  the  sides 
and  top  of  the  retort, 
the  strips  being  built 
into  each  cross- wall  as 
it  goes  up.  As  the  tem- 
perature of  the  setting 
is  gradually  raised,  the 
wood  chars,  and  finally 
burns  completely  away 

when  the  working  heats  are  obtained,  thus  providing  a  small  space  for  expansion, 
and  preventing  undue  pressure  on  the  retort.  Owing  to  the  liability  of  retorts 
immediately  surrounding  the  combustion  chamber  to  suffer  from  the  severe  and 
sometimes  local  heating  at  this  point,  it  has  for  some  time  been  the  practice'  to 
insert  special  silica  protection  shields  (as  shown  in  Fig.  93)  around  the  bottom 
corners.  At  the  same  time  the  silica  material  is  liable  to  be  affected  by  the  slag- 
ging action  of  the  dust  carried  forward  by  the  furnace  gases ;  and,  for  this 
reason,  the  block  illustrated  in  Fig.  94  has  in  some  cases  been  adopted.  This 
shield  is  made  wholly 
from  Stourbridge  clay, 
of  the  same  material  as 
the  retorts,  and  will  fre- 
quently be  found  to  out- 
last the  retorts  them- 
selves. The  main  body 
of  the  block  is  3  inches 
in  thickness,  and  it  is 
made  of  such  a  length  as 
to  run  from  centre  to 
centre  of  the  cross  divi- 
sion walls  from  which  it 
is  supported. 

Another     successful 
idea,  which  has  been  in- 
troduced   with    a    view 
both  to  economy  and  the     FIG.  93. — SEGMENTAL  RETORT,  21  INCHES  x  15  INCHES,  WITH  ROUND 
protection  of   the   retort,  SPRINGER  AND  SHIELD  ON  COMBUSTION  CHAMBER,  SIDE  AND 

SQUARE  SPRINGER  ON  EXTERNAL  SIDE.    THE  LENGTH  OF  THE 
IS  that  shown  in   Fig.  95.  SEGMENTS  VARIES  FROM  1  FOOT  3  INCHES  TO  2  FEET. 


REFRACTORY  MATERIALS 


151 


FIG.  94. — FIRECLAY  SHIELD  BLOCK. 


In  the  majority  of  cases 
of  "  through "  retort 
settings  it  is  customary 
to  insert  a  9-inch  cross- 
wall  here  and  there  in 
the  setting,  and  particu- 
larly where  the  retort 
joints  occur.  By  adopt- 
ing the  arrangement 
shown  in  the  sketch,  the 
expense  of  the  heavier 
wall  is  obviated,  and  4£- 
inch  brickwork  (or  cer- 
tainly 6-inch)  can  be  run 
up  instead.  A  9-inch 
ring  of  brickwork  (usu- 
ally Ewell)  is  carried 
completely  round  the 
retort,  and  the  4^-inch 

wall  carried  direct  from  this.     In  the  case  of  those  retorts  surrounding  the  com- 
bustion chamber,  the  brickwork  makes  an  admirable  substitute  for  special  protection 

blocks. 


COMBUSTION 

CHAMBER    AND 

CROSS -WALLS 

The  greatest  in- 
tensity of  heat  which  is 
produced  in  a  retort  set- 
ting is  in  the  combustion 
chamber  and  [its  imme- 
diate neighbourhood ; 
hence  a  material  of  high 
refractory  qualities  is 
essential.  In  this  respect 
the  siliceous  or  silica 
materials  are  to  be  pre- 
ferred, and  those  of  the 
Dinas  type,  containing 

upwards  of  96  per  cent,  of  silica,  are  now  coming  into  fairly  general  use  for  the 
purpose.  In  this  connexion  it  is  always  well  to  bear  in  mind  that  while  fireclay  of 
the  aluminous  or  Stourbridge  type  shows  some  tendency  to  contract  when  under 
working  heats,  the  clays  known  as  siliceous  invariably  expand  ;  and,  as  a  general 
rule,  the  higher  the  silica  content  the  greater  will  this  tendency  be.  Bricks  of  the 


FIG.  95. — 4^-iNCH  DIVISION  WALL  WITH  9-iNCH  EWELL  RING. 


152 


MODERN  GASWORKS  PRACTICE 


Ewell  type,  however,  being  intermediate  so  far  as  silica  content  is  concerned  (87  to 
89  per  cent.),  remain  practically  stationary,  although  at  the  more  intense  heats 
there  may  be  some  slight  tendency  towards  expansion.  Owing  to  this  property, 
also  to  their  high  refractoriness,  the  Ewell  bricks  are  largely  used  for  combustion 
chambers  and  cross  walls  in  modern  settings. 

The  characteristic  of  certain  bricks  to  diminish  or  increase  in  size  is  rather 
liable  to  upset  the  calculations  of  those  responsible  for  the  design  of  settings,  one 
of  the  chief  consequences  being  that  the  retorts,  after  a  short  time,  fall  slightly 
out  of  level.  '  In  order  to  avoid  this,  an  arrangement  has  been  introduced  by  some 

engineers  whereby  the  varying  properties  of  the 
two  types  of  material  are  made  to  neutralize  one 
another.  For  instance,  the  furnace  arch  and  com- 
bustion chamber  may  be  built  up  of  silica  ware 
and  the  division  walls  of  material  having  a  con- 
tracting nature.  On  heating  up,  the  expansion 
of  the  former  is  counteracted  by  the  contraction 
of  the  latter — hence  everything  is  maintained  on 
an  even  keel.  A  setting  built  up  in  this  way  is 
diagrammatically  shown  in  Fig.  96. 

Attention  must  be  drawn  to  the  practice  of 
running  up  the  cross- walls  between  the  retorts  and 
above  the  combustion  arch  of  siliceous  material, 
while  on  the  outer  side  of  the  setting,  where  the 
heat  is  less,  the  same  walls  are  continued  in 
aluminous  work.  In  such  cases  it  is  frequently 
found  that  the  retorts  tend  to  overturn  in  an 
outward  direction  (particularly  if  the  joints  in 
the  wall  have  been  made  fine),  this  being  due 
to  the  pushing  upwards  and  outwards  of  the  silica 
material,  whereas  the  aluminous  material  on  the 
outside  will  have  undergone  a  certain  amount  of 
shrinkage,  thus  allowing  the  movement  to  take 
place.  In  the  construction  of  all  types  of  division 
walls,  it  will  be  found  an  excellent  policy  to  leave 
a  big  joint  here  and  there  to  take  up  the  crowding  out,  if  necessary.  With  regard 
to  these  cross-walls,  it  must  be  remembered  that,  so  far  as  the  greater  portion 
of  them  is  concerned,  mechanical  strength  is  desirable  rather  than  extreme  re- 
fractoriness, for  the  material  merely  comes  in  contact  with  the  circulating  gases, 
and  is  not  likely  to  be  affected  by  any  severe  cutting  heat.  Consequently,  a  brick 
of  greater  density  and  less  porosity  may  be  used,  and  ordinary  Stourbridge  fire- 
bricks of  the  best  quality  usually  give  every  satisfaction.  Speaking  of  "  cutting 
heats,"  it  is  as  well  to  point  out  that  small  combustion  chambers,  although  they 
have  their  advocates,  are  decidedly  conducive  to  these,  and  also  prevent  the 
effective  mixing  of  the  gases. 


Scotch—  Contracts 


flHI    Oinas  —  Expands 

I1    i    '  I    Stourbridge  —  Contracts 

FIG.  96. — COMPENSATION  ARRANGE- 
MENT FOB  EXPANSION  AND  CON- 
TRACTION. 


REFRACTORY   MATERIALS  153 

Bywater  has  drawn  attention  to  the  necessity  of  employing  bricks  for  the  cross- 
walls  which  are  of  sufficient  refractoriness  to  withstand  the  working  temperature, 
:as  drippings  resulting  from  the  fusion,  or  partial  fusion,  of  these  often  cause  trouble. 
He  further  recommends  the  use  of  high-class  bricks  of  the  Glenboig,  Ganister, 
Stourbridge,  or  Yorkshire  and  Derbyshire  biscuit  silica  as  being  quite  suitable 
and  desirable. 

The  disastrous  effect  which  a  small  proportion  of  alkaline  impurities  may  have 
on  the  remainder  of  the  setting  has  already  been  emphasized.  It  is  well  known, 
of  course,  that  in  the  case  of  the  ordinary  stock  building  brick  the  original  clay 
contains  a  comparatively  high  proportion  of  impurities,  and  these  are  actually 
caused  to  flux  during  burning  so  as  to  firmly  bind  the  remainder  of  the  material 
together.  A  point  to  remember  is  that  extremely  high  .temperatures  and  "  cut- 
.ting  heats  "  are  not  alone  responsible  for  "  running."  Considerable  damage  from 


FIG.  97. — THE  EFFECTS  OF  "  RUNNING. 


this  cause  may  often  be  found  at  the  relatively  cool  zone  of  the  producer  linings, 
and  also  at  the  base  of  water-gas  generators.  Such  occurrences  are,  of  course, 
due  to  the  adhesion  of  clinker  (having  an  extremely  low  fusion  point)  to  the  walls, 
and  its  subsequent  "  slagging  "  action  on  the  impurities  of  the  lining  material.  The 
chief  precaution  is  to  ensure  that  the  bricks  or  blocks  made  use  of  contain  a  low  pro- 
portion of  fusible  constituents.  The  unwelcome  results  of  "  running  "  are  very 
well  illustrated  in  Fig.  97.  This  photograph  shows  the  consequences  of  using 
an  unsuitable  jointing  material,  and  the  manner  in  which  incipient  slagging  has 
been  set  up  in  the  brick  can  be  clearly  noticed.  The  brick  in  this  case  was 
taken  from  a  combustion  chamber  working  at  a  temperature  of  about  2,600° 
Fahr. 

With  regard  to  fireclays  for  the  making  of  cement  for  use  in  retort  benches,  before 
making  a  definite  purchase  it  is  advisable  to  apply  a  rough  test  in  order  to  ascertain 
their  suitability.  An  excellent  rough  method  for  determining  their  refractoriness 


154 


MODERN   GASWORKS   PRACTICE 


is  to  mix  up  the  cement  in  the  usual  way,  afterwards  plastering  it  on  one  side  of 
a  brick  to  the  depth  of  about  an  inch.  The  brick  should  then  be  pushed  into  the 
combustion  chamber  of  a  retort  setting  and  allowed  to  remain  for  about  a  week. 
If  at  the  end  of  that  time  there  is  no  sign  of  fusion,  the  material  may  be  safely  relied 
on.  The  test  is,  no  doubt,  severe — particularly  in  view  of  the  rapid  rate  at  which 
the  temperature  of  the  sample  is  increased. 

PRODUCERS  AND  REGENERATORS 

As  pointed  out  above,  the  material  employed  for  the  lining  of  the  producer 
must  possess  the  ability  to  withstand  the  slagging  action  of  the  low  fusing-point 
impurities  associated  with  the  fuel.  It  is  a  recognized  rule  of  retort-house  practice 
that  the  furnaces  must  not  be  too  hot ;  therefore  there  is  theoretically  no  need 
for  very  high  refractoriness.  If,  however,  an  inferior  brick  were  made  use  of,  the 
results  would  undoubtedly  be  very  far  from  pleasing,  for  the  heat  in  the  producer 
— chiefly  owing  to  fluctuation  in  the  depth  of  the  fuel  bed — undergoes  severe  changes. 

With  regard  to  the  construction  of  the  regenerator  flues  for  the  circulation 
of  secondary  air  and  waste  gases,  it  must  be  borne  in  mind  that  the  arrangement 
is  employed  with  a  view  to  abstracting  the  maximum  of  heat  from  the  waste  gases 
and  conducting  it  to  the  secondary  air.  Accordingly,  as  the  heat  to  be  withstood 
is  comparatively  low,  the  bricks  or  blocks  should  be  made  with  an  eye  to  high  thermal 
conductivity  and  mechanical  strength  rather  than  to  high  refractoriness. 


OUTSIDE  WALLS  AND   INSULATION 

The  chief  qualities  required  of  the  material  of  which  the  outside  or  front  walls  of 
the  setting  are  composed  are  moderate  refractoriness,  but,  more  especially,  a  low 
ability  to  conduct  heat.  By  far  the  most  common  practice  is  still  that  of  building 
up  these  walls  of  9-inch  or  13^-inch  work  in  aluminous  fireclay, 
but  within  the  last  few  years  some  attempt  has  been  made  to 

•  reduce  the  thermal  losses  by  radiation  from   these  walls   to  a 

minimum.     Chief  among  these  methods  is  that  of  building  up 
^     a  cavity  wall  (a  clear  2-inch  space  usually  being  left,  whilst  for 
_  s<^        the  sake  of  stability  the  two  walls  are  tied  together  at  intervals 
•  by  a  brick),  the  cavity  being  left  clear,  or  filled  in  with  some 

type  of  non-conducting  material,  such  as  asbestos  composition. 
}s     A  more  recent  means  is  to  fill  in  the  cavity  or  to  build  up  a 
*^         separate  interior  wall  from  one  of  the  special  types  of  insulat- 

ing bricks,  such   as   the    "  Thermalite  "    or    "  Moler."     These 
?  .  .       ,  .  ,  , 

FOR  bricks  are  extremely  light,  thus  indicating  high  porosity  and 

OUTSIDE  WALL  OF  jow  conductivity.       On  the  Continent,  a  practice  is  in    vogue 

by  which  the  entire  outside  wall  is  constructed  of  large  hollow 

blocks  as  shown  in  Fig.  98.     In  the  case  where  a  screening  wall  of  some  type  of 

insulating  material  is  employed,  there  seems  little  reason  why  the  face  wall  of  the 

setting  should  not  be  built  up   entirely  from   ordinary   stock  brickwork.      Such 


FIG.     98.—  SPECIAL 
AIR-BLOCKS 


REFRACTORY  MATERIALS  155 

bricks,   owing  to  their  relatively  high  porosity,  would  ensure  the  retention  of  a 
further  amount  of  heat. 

APPROXIMATE  MELTING  POINTS  OF  VARIOUS  SUBSTANCES 

Chromite           .          .  *       .          .          .          .          .          .         .         •.  .  3,950°  Fahr. 

Magnesia  brick                .    .•         .         .          ,         .         „         ,         .  .  3,930°       „ 

Chromite  brick          .          .          .         „          ,         ,         ,         ,.        ,  .  3,722° 

Pure  alumina  .          .          .         .  .          .          ,         ,  3,650°       „ 

Bauxite  clay    .          .          .         .         .          .          .          ,         .        ".  ,      .  3,260° 

Pure  silica        .          .          . -. -..       ,      -   .  .  3,200° 

Kaolin     .          ... .  3,160° 

Silica  brick      .         .  ,                ,     '.         ;.  .  3,090° 

Fireclay  brick.         ,         .        -,         ,         .         .         ,         ,         ,  .  2,900° 


CHAPTER   VII 
RETORT-BENCH   APPURTENANCES 

THE  retort-bench  fittings  employed  with  modern  horizontal  settings  do  not  vary  in 
•character  to  any  marked  extent.  Various  engineers  employ  different  means  for 
arriving  at  the  same  end ;  but  the  distinction  in  most  cases  is  generally  a  matter 
•of  detail.  In  the  first  place,  the  chief  items  requiring  consideration  are  : — 

1.  (a)  The  primary  staying- up  of  the  bench  (i.e.,  by  longitudinal  and  transverse 

buckstays  and  ties). 

(6)  The  secondary  staying-up  of  the  individual  setting,  such  as  cross-bracing 
between  the  buckstays  to  prevent  protrusion  of  the  regenerators  and 
the  producer  front.  Also  the  bracing  of  the  front  walls  above  the  pro- 
ducer, and  the  retention  and  support  of  retort  mouthpieces  in  their 
correct  position. 

2.  In  addition,  consideration  has  to  be  given  to  the  various  features  in  the 
'design  and  erection  of  the  retort  mouthpieces,  ascension  pipes,  bridge  pipes,  hydraulic 
mains,  etc.,  so  that  the  process  of  gas  making  may  proceed  with  the  regularity  essen- 
tial to  the  best  results. 

RETORT  MOUTHPIECES 

The  self-sealing  metal-to-metal  retort  door  is  now  in  almost  universal  use,  except 
in  the  smallest  of  works  making  less  than  about  6  to  8  million  cubic  feet  of  gas  per 
;annum,  which,  for  the  sake  of  convenience,  still  adhere  to  the  detached  door  with 
.spent  lime  luting  and  central- tightening  hand-screw.  For  small  stop-ended  retorts 
this  method  is  advisable,  particularly  in  cases  where  no  facilities  exist  for  re- 
adjusting the  self-acting  type.  As  the  means  wherewith  hermetical  sealing  is 
obtained  in  the  common  type  of  door  are  not  always  fully  understood,  a  diagram 
(Fig.  99)  is  given  showing  the  principle  employed.  First,  the  tightening  handle 
is  forged  with  two  eccentrics,  as  shown  in  Fig.  100,  and  the  cross-bar  passing  in 
front  of  the  lid  turns  on  these  eccentrics.  At  the  same  tune,  when  the  tightening 
handle  is  turned  it  revolves  about  the  centre  of  rotation  shown.  It  is  thus  seen 
that  the  eccentrics  force  the  cross-bar  towards  the  lid,  and  the  bar — turning  on  the 
fulcrum  formed  by  the  clip  B — transmits  pressure  to  the  centre  of  the  door  at  A. 
By  means  of  an  eccentric  bolt,  with  which  the  cross-bar  is  attached  to  the  rib  of  the 
door  at  A,  wear  can  be  taken  up  and  the  pressure  regulated.  With  the  Q -shaped 

156 


RETORT-BENCH  APPURTENANCES 


157 


door  the  pressure  is  not  applied  at  the  true  centre,  hence  it  is  greater  at  certain 
portions  of  the  faced  rim  than  at  others,  this  being  an  objectionable  but  unavoidable 
feature  of  the  appliance. 

The  means  employed  for  attaching  the  mouthpiece  to  the  retort  is  of  consider- 


Centre  -oJ  Rotation 


of  Tightening  Handle 


Detail  of  Eccentric  and  Cross  Bar 


FIG.  99. — SELF- SEALING  RETOKT  LID,  SHOWING 
PRINCIPLE  OF  ACTION. 


FIG.  100. — DETAIL  OF  TIGHTENING 
HANDLE,  SHOWING  ECCENTRICS. 


able  importance,  as  an  insecure  joint  soon  gives  way  under  the  stresses  of  the  stoking 
machinery  and  pipe  augering.  There  are  three  distinct  methods  now  made  use  of 
for  affixing  the  mouthpiece.  The  most  common  method  (Fig.  101)  is  to  cast  the 
mouthpiece  with  a  plain  back  flange,  the  flange  being  drilled  at  intervals  for  bolts, 
which  are  secured  in  slots  in  the  thickened  end  of  the  retort.  In  this  case  some 
form  of  jointing  material  must  be  used  between  the  flange  and  fireclay  end  of  the 
retort,  for  which  purpose  the  following  usually  gives  the  best  results:  One  part 
of  cast  iron  borings  to  2|  parts  of  fireclay,  the  mixture  being  just  damped  with  a 
solution  of  sal  ammoniac.  The  amount  of  sal  ammoniac  required  is  about  1  Ib. 
to  every  hundredweight  of  the  fireclay  and  borings.  For  this  purpose  sal  ammoniac- 
is  to  be  preferred  to  ammoniacal  liquor,  as  a  more  complete  rusting  action  is  set  up. 


FIG.   101.  —  COMMON     FIG.  102.— SHEATH  FIG.  103.— C.  I.  SHEATH.     FIG.  104.— SHEATH  AND 

BOLT  ATTACHMENT.  ATTACHMENT.  MOUTHPIECE  COMBINED. 

METHODS  OF  ATTACHING  MOUTHPIECES  TO  RETORTS. 

A  comparatively  recent  method  of  attachment  is  that  shown  in  Fig.  102,  in 
which  a  distinct  sheath  or  socket  is  employed.  The  socket  (Fig.  103)  is  made  from 
cast-iron,  usually  f  inch  thick  throughout,  and  is  passed  completely  over  the  end  of 


158 


MODERN   GASWORKS   PRACTICE 


the  retort,  extending  about  8  inches  backwards.  In  this  case  the  end  of  the  retort 
is  not  thickened  up,  the  lengths  as  laid  having  3-inch  walls  throughout ;  and  as  a 
fairly  tight  fit  is  arranged  for  (slight  chipping  of  the  fireclay  end  often  being  necessary), 
no  rust  joint  is  employed,  but  the  retort  is  given  a  wash  of  fireclay  before  the  socket 
is  fitted.  Bolts,  countersunk  on  the  inside  of  the  socket,  form  the  attachment 
for  the  ordinary  mouthpiece  flange.  The  chief  merits  of  the  method  are  that  the 
retort  mouthpiece  can  be  easily  removed  for  repairs,  the  holding  bolts  are  far  less 
liable  to  burn  or  break  away  than  with  the  common  type  of  attachment,  and,  if  pro- 
perly fitted,  a  tighter,  and  at  the  same  time  more  elastic,  joint  is  obtained. 

The  third  method  (Pig.  104)  is  comparatively  rare  in  this' country,  but  possesses 
the  advantage  that  no  retort  bolts  whatever  are  required.  It  is  really  another 
means  of  carrying  out  the  socket  principle  described  above,  with  the  difference  that 
some  initial  expense  is  saved  by  casting  the  socket  and  mouthpiece  in  one.  Its 
disadvantage,  however,  lies  in  the  fact  that  the  security  of  the  mouthpiece  is  entirely 
dependent  upon  the  cross  bracing  employed  (although  the  latter  can  be  made  more 
effective  owing  to  the  absence  of  protruding  bolts)  and  the  socket  portion  has  a 
tendency  to  crack.  Once  such  a  crack  develops  it  is  difficult  to  prevent  a  certain 
amount  of  gas  leakage  when  the  retort  is  under  pressure. 

In  addition  to  the  bolt  attachment,  all  retort  mouthpieces  must  be  stayed  up 
by  means  of  bracing  attached  to  the  main  buckstays,  and  passing  outside  the  front 
wall  of  the  setting  across  the  flanges  of  the  mouthpieces.  There  are  several  means  of 
attaching  such  bracing,  the  most  common  being  shown  in  Figs.  105  and  106.  In 


R    S    J 

Buckstay 


FIG.  105.— C.  I.  BRAC- 
KET FOR  SUPPORTING 
BRACING  RAIL  FOR 
RETORT  MOUTH- 
PIECES. 


FIG.'  106.— C.  I.  BRAC- 
KET FOR  CHANNEL 
IRON  MOUTHPIECE 
BRACING. 


FIG.  107.  -  -  SINGLE 
BULL-HEAD  RAIL 
SUPPORT. 


!Fig.  105  a  double  bull-headed  rail  is  carried  in  cast-iron  brackets  attached  to  the 
buckstays  as  shown.  In  many  cases  the  rail  is  carried  across  vertically  (as  shown 
dotted),  so  that  an  ample  bearing  on  the  lower  portion  of  the  flange  of  one  mouth- 
piece and  the  upper  portion  of  the  flange  of  the  mouthpiece  just  below  may  be  ob- 
tained. The  arrangement  given  in  Fig.  107,  although  frequently  seen,  is  not  to  be 
recommended,  particularly  in  view  of  the  fact  that  the  main  buckstays  do  not  bear 
direct  upon  the  brickwork  of  the  bench,  an  intervening  space  being  left  which  is 
filled  in  with  a  false  wall. 


RETORT-BENCH   APPURTENANCES  159 

ASCENSION   PIPES,   BRIDGE   PIPES,   AND    DIP   PIPES 

The  point  of  chief  importance  with  regard  to  the  ascension  pipe  is,  perhaps, 
its  size.  Present-day  practice  in  this  respect  is  towards  ample  area,  so  much  so 
that  in  many  cases  the  pipes  in  modern  installations  provide  practically  double  the 
cross-sectional  area  considered  sufficient  a  decade  ago.  In  general,  however,  design 
may  be  considered  on  safe  lines  if  carried  out  in  accordance  with  the  following  : — 

SIZE  OF  ASCENSION   PIPES 

Works  making  under  10  million  cubic  feet  per  anoum  .          .          .     5-inch  pipe. 

Works  making  between  10  million  and  200  millioncubic  feet  per  annum     6       „       „ 
Works  making  above  200  million  cubic  feet  per  annum         .          ..         .7       „.       ,, 

This  rule  refers,  of  course,  to  retorts  having  an  ascension  pipe  at  each  end,  in 
the  case  of  "  through  "  settings.  In  a  recent  horizontal  bench,  ascension  pipes  of 
8-inch  diameter  have  been  fitted  at  each  end  of  the  retort.  The  chief  difficulty  with 
the  larger  pipes  lies  in  inducing  the  attendants  to  clear  them  properly.  For  7-inch 
pipes  a  5£  or  6-inch  auger  is  generally  used,  but  above  this  size  the  augers  become 
somewhat  unwieldy  and  difficult  to  handle,  so  that  there  is  some  temptation  to 
make  use  of  them  as  little  as  possible.  In  the  arrangement  of  ascension  pipes  it  is 
necessary  to  keep  them  as  far  as  possible  from  the  centre  of  the  setting,  so  that  they 
are  unaffected  by  the  heat  of  the  combustion  chamber.  There  is  also  the  question 
of  curvature,  for  the  purpose  of  working  round  the  upper  mouthpieces.  All  abrupt 
bends  must  be  rigidly  avoided,  otherwise  endless  trouble  in  cleaning  the  pipes  and  in 
the  prevention  of  stoppage  will  ensue.  Further,  precaution  must  be  taken  to  see 
that  the  jointing  material  used  in  the  pipe  sockets  is  not  allowed  to  get  past  the 
spigot  end,  and  thus  be  responsible  for  projections  which  partly  stop  the  pipe  and 
provide  a  lodgment  for  the  formation  of  pitchy  deposits.  So  far  as  the  general 
arrangement  is  concerned,  as  many  of  the  pipes  as  conveniently  possible  should 
be  carried  up  on  the  sides  of  the  main  arch  nearest  its  springings,  and  it  is  necessary 
to  avoid  running  up  two  pipes  between  any  two  mouthpieces,  otherwise  the  retorts 
will  have  to  be  spaced  wider  apart  in  order  to  give  sufficient  room,  this  tending  to 
spoil  the  heating  arrangements  of  the  interior. 

The  joints  in  ascension  pipes  must  on  no  account  be  made  with  lead.  Although 
rust  joints  of  iron  borings  are  not  essential,  they  are  to  be  preferred  to  any  other 
material,  in  spite  of  the  additional  labour  entailed  in  cutting  them  out  during  dis- 
mantling. For  ascension-pipe,  bridge- pipe,  and  dip-pipe  joints  the  following  material 
may  be  used  : — 

Cast-iron  borings  damped  down  with  gas  liquor,  rammed  well  into  the  joint, 
and  left.  When  the  bench  is  got  to  work,  the  heat  from  the  setting  quickly  hardens 
off  the  joint. 

Where  borings  are  only  obtained  with  difficulty,  or  to  save  expense,  a  very 
serviceable  joint  can  be  made  from  the  following  mixture  : — 

Ewell  brick  dust    .          .          .          .          .          .          .          .          .          .          .1  part. 

Slaked  lime    .          .          .          .          .          .          .....          .          .2  parts. 

This  is  rammed  into  the  joint  dry,  no  moistening  whatever  (beyond  the  slaking 


160 


MODERN   GASWORKS   PRACTICE 


of  the  lime)  being  necessary.     In  cases  where  a  cast-iron  foul  main  is  used,  lead! 
joints  may  safely  be  used  in  the  sockets,  and  are  desirable. 

STOPPED   PIPES 

The  introduction  into  the  larger  works  of  the  mass  system  of  carbonization  has. 
proved  the  most  effective  deterrent  to  the  old-time  trouble  of  continually  stopped 

ascension  pipes.  The  absence  of  pitchy  deposits  may  be  chiefly  attributed  to  the 
lower  temperature  of  the  escaping  gases  and  the  increased 
velocity  with  which  they  travel  through  the  pipe.  In 
addition,  the  elimination  of  an  excessive  "  free  space  "  in 
the  retort  accounts  for  less  degradation  of  the  hydrocar- 
bons, with  the  result  that  a  minimum  quantity  of  free 
carbon  is  carried  forward  in  suspension  by  the  gas.  It  is: 
such  solid  particles  (also  those  drawn  up  from  the  cloud 
of  coal  dust  inseparable  from  some  types  of  charging 
machines)  which,  by  adhering  to  the  tarry  surfaces  of 
the  interior  of  the  pipe,  promote  obstruction.  Once 
started,  such  obstruction  grows  apace. 

When  the  temperature  of  the  issuing  gases  is  high — 
such  as  with  light  charges  or  layer  carbonization — the 
escaping  tarry  vapours  undergo  distillation  and  redistilla- 
tion in  the  pipe  until  a  pitchy  mass  capable  of  no  further- 
volatilization  remains.  The  most  satisfactory  means  to 
avoid  stoppage  is  to  ensure  that  every  pipe  is  augered  each 
time  the  retort  is  opened  for  charging,  whether  there  is  any 
apparent  obstruction  or  not.  Some  engineers  prefer  to 
arrange  for  an  auger  gang  to  pass  right  through  a  definite 

row  of  pipes  an  hour  or  so  before  the  charges  are  withdrawn.     In  this  way  the 

work  of  charging  and  drawing  is  not  delayed,  and  it  is  claimed  that  the  time  is 

favourable  for  the  operation  owing  to  the  condition  of  the  tarry  mass. 
Many  ideas  have  been  introduced   with  the 

object  of  avoiding  trouble  from    stopped   pipes, 

and  one  of  the  foremost  of  these  was  the  admission 

of   a  small  trickle  of  water  to  the  apex  of  the 

ascension  pipe  by  means  of  a  gooseneck  (Fig.  108), 

or  by  the  Darwen  pipe  (Fig.  109).     In  this  way 

the  temperature  of  the  pipe  is  lowered,  whilst  the 

steam  produced  aids  in  carrying  away  a  portion 

of  the  tarry  vapours  before  their  distillation  can 

take  place.      Another  means  of    arriving  at  the 

same  result  is  to  add  a  small  proportion  of  water 

to  the  coals  before  carbonization,  but  some  considerable  loss  in  gas  "  make  "  may 

follow  such  procedure.     In  some  cases  a  small  steam  supply  has  been   admitted' 

direct  to  the  base  of  the  pipe,  but  its  use  appears  to  be  attended  with  mixed' 


FIG.  108.  —  WATER-FEED 
FOB  ASCENSION  PIPE. 


Supply  Ta 


FIG.  109. — THE  DARWEN  PIPE. 


RETORT-BENCH  APPURTENANCES  161 

results.  A  precaution,  however,  which  calls  for  attention  is  the  avoidance  of  cut- 
ting draughts  around  the  pipes,  and  local  cooling.  Where  the  latter  occurs  in 
any  degree,  trouble  will  nearly  always  be  experienced  ;  and  in  some  works  provi- 
sion has  been  made  for  ensuring  uniform  temperatures  by  jacketing  the  pipes  with 
non-conducting  material.  This  would  certainly  seem  unnecessary  in  any  but  very 
exceptional  cases ;  but  care  should  be  given  in  the  design  of  the  house  so  that 
draughts  are  avoided,  whilst  ample  room  should  be  left  around  the  ascension  pipes 
for  the  effective  circulation  of  air. 

THE   SINGLE  ASCENSION  PIPE 

In  recent  years  there  has  been  some  tendency  to  work  with  only  one  ascension 
pipe  for  the  removal  of  the  gas  from  a  through  retort,  instead  of  providing  a  pipe 
at  each  end,  as  is  the  more  common  practice.  When  the  single  pipe  is  used  it 
should,  for  the  standard  sizes  of  through  retorts,  never  be  less  than  8  inches  in 
diameter.  The  following  are  the  advantages  which  may  be  claimed  for  the  single- 
pipe  system : — 

(a)  Owing  to  the  necessity  of  providing  only  one  set  of  ascension  pipes,  dip 
pipes,  hydraulic  main,  tar  towers,  foul  main,  etc.,  to  each  retort  setting,  the  saving 
in  initial  cost  is  considerable.  It  must  be  remembered,  however,  that  two  hydraulic 
mains  should  be  used  when  there  are  ten  or  more  retorts  to  the  setting,  also  with 
settings  of  "  eight  "  in  two  rows.  This  is  owing  to  the  available  width  of  the  arch. 

(6)  There  are  fewer  pipes  to  keep  clear.  At  the  same  time  the  pipes  are  larger, 
and  the  labour,  therefore,  is  more  arduous.  When  the  pipes  are  all  on  one  side, 
the  men  can  keep  away  from  the  stoking  machinery,  and  are  thus  out  of  the  way, 
whilst  there  is  less  liability  of  coal  dust  being  carried  up  the  pipe. 

(c)  There  is  said  to  be  greater  immunity  from  stopped  pipes. 

(d)  There  is  said  to  be  an  improvement  in  gas  yield  and  quality. 

With  regard  to  statements  (c)  and  (d),  they  must  be  taken  with  a  certain 
amount  of  reserve,  as  experience  with  single  pipes  has  hardly  been  such  as  to  definitely 
establish  these  facts.  The  disadvantages  of  the  system  are  : — 

(a)  It  cannot  satisfactorily  be  employed  when  the  retorts  are  fully  charged,  for 
although  a  vacuum  may  obtain  in  the  end  of  the  retort  nearer  the  pipe,  there  is 
likely  to  be  a  heavy  pressure  at  the  other  end,  owing  to  the  gas  way  being  choked 
by  swelling  of  the  coal,  uneven  charging,  etc. 

(6)  With  light  charges  the  gas  travelling  from  the  farther  end  of  the  retort  is 
in  contact  with  the  hot  walls  for  a  considerably  longer  period  than  is  the  case  when 
two  pipes  are  employed.  Hence  excessive  degradation  is  probable. 

(c)  If  the  single  pipe  becomes  choked  there  is  no  alternative  outlet  for  the  gas  ; 
but,  as  previously  noted,  no  well-managed  works  should  have  a  completely 
choked  pipe. 

BRIDGE   PIPES 

The  change  of  direction  of  flow  of  the  gas  from  the  ascension  pipe  to  the  dip 
pipe  is  effected  by  means  of  the  bridge,  arch,  or  saddle  pipe.  When  direction  has 

M 


162 


MODERN   GASWORKS   PRACTICE 


to  be  altered  in  this  manner  a  certain  amount  of  friction  is  inevitable.  The  change 
must  be  effected  as  gradually  and  smoothly  as  possible,  so  as  to  avoid  mechanical 
deposition  of  the  tarry  vapours  and  suspended  particles.  To  this  end  sharp  angles 
must  be  avoided.  An  equally  important  feature  in  connexion  with  the  bridge  pipe 


FIG.  110. 


FIG.  111. 


FIG.  112. 


is  that  of  ensuring  easy  access  to  all  sections  of  the  pipe  way.  Various  types  of 
bridge  pipes  are  illustrated  (Figs.  110  to  115).  Fig.  110  is  chiefly  found  in  the 
smaller  works.  The  design  shown  in  Fig.  112  should  be  avoided,  for,  in  spite  of 
easy  access  to  all  sections,  the  change  of  direction  is  far  too  abrupt.  The 


FIG.  113. 


FIG.  114. 
THE  BOURNEMOUTH  TYPE. 


FIG.  115. 
FOR  VERTICAL  RETORTS. 


"  Bournemouth  "  type  embraces  many  advantages,  chief  among  these  being  the 
means  of  cleaning,  both  branches  being  accessible  by  the  removal  of  a  single  flange, 
and  that  not  a  cumbersome  one.  The  joints  of  bridge  pipes  should  be  made  of 
similar  material  to  that  employed  for  ascension  pipes.  In  the  "  Darwen  "  pipe 
(Fig.  109)  a  large  expansion  and  cooling  chamber  is  provided  at  the  top  of  the 
ascension  pipe,  whilst  the  top  of  the  bridge  forms  a  water-supply  tank  which  feeds 
a  drip  cock  immediately  above  the  rising  pipe. 

DIP  PIPES 

Dip  pipes  may  be  connected  to  the  bridge  pipe  by  means  of  either  flange  or 
socket  joints  ;  the  latter  are  the  more  common.    The  pipe  is  always  connected  to  the 


RETORT-BENCH   APPURTENANCES  163 

hydraulic  main  by  a  flange.     Although  in  many  cases  the   seal 
end  of  the  dip  pipe  is   left  square,  it  is   now  generally  recog-  ~|~' 
nized  that  more  effective  working  ensues  if  it  is  turned  to  a  u 
knife  edge,  as  seen  in  Fig.  116.     By  this  means  less  oscillation  of  _{_ 
the  liquor  takes  place,  the  gas  spreads  more   effectively,  and     $ia.  116.   FIG.  117. 
suspended  tar  vesicles  are  more  easily  removed.     For  the  last- 
named  reason  some  engineers  prefer  the  serrated  end  as  in  Fig.  117. 

Some  care  is  necessary  during  the  erection  of  dip  pipes  in  order  to  ensure  that 
the  seal  on  each  will  be  the  same.  Providing  the  hydraulic  mains  have  been  laid 
on  a  perfectly  even  keel,  a  uniform  seal  may  be  best  obtained  by  machining  a  small 
portion  of  the  upper  face  of  the  dip-pipe  flange.  When  turning  up  the  dip  edges 
the  distance  (d),  Fig.  116,  can  be  made  constant  for  all  pipes.  When  the  pipes  are 
in  position,  ready  to  be  permanently  tightened  down,  a  straight  edge  can  be  run 
along  the  turned  portion  of  all  flanges.  So  long  as  the  straight  edge  remains  level 
the  dip  pipes  will  then  all  be  level  at  the  lower  edges,  and  any  flanges  not  complying 
with  the  line  of  level  can  be  there  and  then  adjusted.  This  method  is  preferable  to 
running  a  straight  edge  underneath  the  dips  and  inside  the  hydraulic  main ;  and, 
if  necessary,  the  dips  throughout  the  whole  house  can  be  brought  to  a  common  level 
with  ease. 

When  a  retort  bench  is  picked-up  from  cold,  some  means  must  be  pro- 
vided for  permitting  any  slight  movement  of  the  ascension  and  bridge  pipes.  This 
may  be  allowed  for  by  making  one  of  the  socket  joints  (preferably  that  where  the 
bridge-pipe  and  dip-pipe  meet)  of  slag  wool  to  a  depth  of  about  2  inches  in  the 
socket.  This  will  permit  movement ;  and  when  the  heats  are  fully  raised,  the 
remainder  of  the  joint  may  be  made  with  borings  in  the  usual  way. 

THE   HYDRAULIC  MAIN 

Although  there  are  still  many  cast-iron  hydraulic  mains  in  use,  they  are  now 
never  erected  where  renewals  or  extensions  are  carried  out.  Mild  steel  plates  put 
together  with  the  aid  of  angle  sections  are  the  modern  practice,  the  plates  being 
from  -^  inch  to  -^  inch  thick,  the  usual  being  f  inch.  With  regard  to  covers,  cast- 
iron  is  still  in  many  cases  employed  with  the  steel  main,  the  reason  being  that  owing 
to  the  numerous  holes  for  dip  pipes  and  bolts  for  flanges  the  steel  cover  is  somewhat 
more  costly,  and  is  apt  to  spring  unless  stiffened.  The  steel  hydraulic  main  is  rarely 
made  square  in  section,  favourite  designs  being  those  of  a  O-shape  or  with  semi- 
circular bottom  as  at  A  in  Fig.  118.  From  every  point  of  view,  however,  the  type 
shown  in  Fig.  119  may  be  looked  upon  as  the  most  effectual.  The  base  is  given  a 
decided  fall  to  the  tar  outlet  pipe  connecting  with  the  tar  main  or  tower ;  and,  in 
addition,  the  main  is  sloped  longitudinally  to  the  same  pipe,  so  that  in  elevation  it  is 
V-shaped.  One  of  the  most  important  features  is  the  apron  plate,  as  seen,  which 
permits  of  the  thorough  cleaning  away  of  pitch  or  other  deposits  which  may  tend 
to  block  the  tar-outlet  pipe.  A  cock,  as  shown,  should  always  be  fitted  to  the  tar 
pipe  from  each  box,  so  that  in  the  event  of  the  cast-iron  pipe  breaking,  the  cocks 
may  be  shut  and  the  unsealing  of  the  dip  pipes  prevented.  If  a  weir  valve  is  em- 


164 


MODERN   GASWORKS   PRACTICE 


ployed,  so  that  gas  and  liquor  pass  out  of  the  box  together,  a  tar  shield,  as 
shown  in  Fig.  120,  should  be  attached  to  the  front  of  the  overflow.  The  heavier 
liquor  and  tar  from  towards  the  bottom  of  the  hydraulic  main  will  then  flow  away 


A  B 

FIG.  118. — METHODS  OF  FIXING  HYDRAULIC  MAINS. 

first.  A  Continental  type  of  hydraulic  main  with  weir  valve  is  illustrated  in  Fig. 
121.  The  main  is  provided  with  cleaning  boxes  fitted  with  automatic  sealing  de- 
vices having  hand- wheel,  screw,  and  locking  bow.  The  special  design  of  tar  shield, 
in  reality  performing  the  duty  of  a  tar  box,  will  also  be  noticed. 

Hydraulic  mains  as  now  erected  are  either : — 
(a)  Distinct  mains,  i.e.,  one  to  every  retort  bench, 

on  either  or  both  sides  ;  or 

(6)  Continuous  mains,  i.e.,  one  uninterrupted  main 
extending  over  a  number  of  (usually  six) 
retort  benches. 

Although  the  latter  type 
is  somewhat  less  expensive  as 
regards  first  cost,  the  advan- 
tages lie  on  the  side  of  the 
distinct  main,  which  is  more 
easily  adjusted.  In  addition, 
a  single  setting  can  be  readily 
isolated,  and  easier  control  is 
assured.  In  many  of  the 
continuous  mains  it  is  customary  to  avoid  the  use  and  expense  of  long  foul  mains 
by  arranging  the  gas  take-off  (or  gas  and  liquor  take-off  over  a  weir  valve)  at 
the  extreme  end  of  one  of  the  sections.  This  method  has,  of  course,  its  advan- 
tages ',  but  one  of  the  chief  troubles  with  hydraulic  mains  is  the  oscillation  of 
the  liquor  therein,  so  that  the  dips  are  alternately  lightly  and  heavily  sealed  as  the 
crests  and  depressions  of  the  waves  pass  around  them.  As  the  "  draw  "  on  the 


FIG.  119. — MODEKN    FOBM 
or  HYDRAULIC  MAIN. 


Shield  \ —    -    - 


FIG.  120. — TAR  SHIELD  FOR 
HYDRAULIC  MAIN. 


RETORT-BENCH   APPURTENANCES 


165 


hydraulic  remains  constant,  the  pressure  or  vacuum  in  the  pipes  connecting  with 
the  retort  is  accordingly  affected  by  considerable  fluctuation.  When,  however,  the 
gas  take-off  is  arranged  at  the  end  of  a  length  of  continuous  main,  the  "  draw  " 


FIG.  121. — HYDRAULIC  MAIN  WITH  ASCENSION  AND  DIP  PIPES,  CLEANING  HOLE,  AND  COMMON  GAS 
AND  TAB  DISCHARGE.    DRORY   SYSTEM. 

from  the  exhauster  appears  to  exert  an  influence  on  the  surface  of  the  long  stream 
of  liquor  and  to  give  rise  to  pronounced  wave-motion. 

Such  is  the  effect  of 
liquor  oscillation  that  vari- 
ous means  have  been  de- 
vised to  restrict  it.  Among 
these  are  Meunier's  floats 
{Fig.  123).  The  floats, 
made  from  wood,  are  placed 
in  the  hydraulic  main  at, 
or  partially  below,  the.  sur- 
face of  the  liquor  and  by  FlGg  122- — CONTINUOUS  HYDRAULIC  MAIN  WITH  END  GAS  AND 
,  /  ,  LIQUOR  TAKE-OFF,  SHOWING  EFFECT  OF  OSCILLATION  DUE 

means  of  a  series  of  holes  TO  EXHAUSTER  PULL. 


166 


MODERN   GASWORKS   PRACTICE 


FIG.  123. 


FIG.  124. 


MEUNIEB'S  FLOATS. 


about  1  inch  in  diameter,  free 
egress  is  provided  for  the  gas. 
It  is  stated  that  a  far  more  uni- 
form level  of  liquid  is  main- 
tained in  the  hydraulic,  there 
is  thorough  contact  between 
the  gas  and  liquid,  and  retort 
pressures  are  more  constant. 
Attached  to  the  floats  are  dip- 
pipe  sleeves  (Fig.  124),  where- 
with the  seal  of  the  pipes  can 
be  either  mechanically  or  auto- 
matically controlled  by  means 
of  rods  passing  through  stuf- 
fing boxes,  as  shown.  The  inventor  states  that  with  the  application  of  the  floats 
he  has  found  an  increase  in  gas  make  of  from  10  to  12  per  cent.,  whilst  the  trouble 
from  naphthalene  is  considerably  curtailed.  The  latter  result  is  said  to  be  due  to 
the  floats  retaining  the  gas  in  longer  contact  with  the  hot  liquid  in  the  hydraulic 
main  than  is  the  case  in  ordinary  working. 

With  regard  to  the  gas  take-off  from  the  hydraulic  mains,  this  should  be  ar- 
ranged from  the  cover  of  the  box,  rather  than  from  the  side,  as  is  so  frequently  found. 
The  method  by  which  the  hydraulic  main  is  supported  in  its  position  above 
the  retort  bench  requires  careful  consideration.  As  the  chief  function  of  the  main 
is  to  provide  a  seal,  it  is  essential  that  it  should  be  maintained  on  a  perfectly  even 
keel ;  hence  the  supports  must  be  such  that  they  are  entirely  uninfluenced  by  any 
movement  of  the  bench  which  may  take  place  when  heating-up  occurs.  In  the  past 
it  was  a  favourite  practice  to  bed  the  main  on  brick  piers  or  cast-iron  standards 
erected  immediately  on  top  of  the  retort  bench ;  thus  when  any  movement  of  the 
latter  occurred  the  mains  were  thrown  out  of  level.  Modern  fixings  for  hydraulic 
mains  which  render  them  entirely  independent  of  the  bench  movements  are  shown 
in  Figs.  118  and  121.  That  shown  at  C,  Fig.  118,  is,  perhaps,  not  so  desirable 
as  the  other  methods,  as  if  tightening  of  the  main  tie  rods  is  necessary,  the 
upper  portion  of  the  buckstays  is  slightly  canted  over,  with  the  result  that  the 
main  may  develop  a  slight  twist.  All  the  methods  are,  however,  subject  to  this 
effect  in  some  degree.  A  very  fine  adjustment  can  be  obtained  by  the  screwed 
supports  shown  in  Fig.  121. 

THE   FUNCTIONS  OF  THE  HYDRAULIC  MAIN 

The  principal  functions  of  the  hydraulic  main  are  : — 

(a)  To  act  as  a  seal  so  as  to  prevent  air  being  drawn  up  the  ascension  pipe 

when  the  retort  doors  are  open. 
(6)  To  act  as  a  safety  seal  in  the  event  of  sudden  heavy  back-pressure  being 

thrown  by  the  apparatus  following,  particularly  in  the  event    of    the 

exhauster  pulling  up. 


RETORT-BENCH  APPURTENANCES  167 

(c)  To  form  a  receptacle  for  the  tar  and  aqueous  vapour  condensed  from  the 
gas  at  the  early  stages  of  manufacture. 

The  seal  on  the  dip  pipes  is,  therefore,  liable  to  be  overcome — 
(a)  by  the  vacuum  induced  by  exhausting ; 

(6)  by  the  stoppage  of  the  exhauster  (or  from  some  other  cause)  and  the  con- 
sequent back-pressure  thrown  on  the  hydraulic  main,  in  which  case 
the  liquor  in  the  main  is  forced  up  the  dip  pipes. 

The  conditions  of  retaining  the  seal  are,  therefore,  dependent  upon  the  relative 
areas  of  the  hydraulic  main  and  dip  pipes.     Theoretically,  if— 

x  —  the  combined  cross- sectional  area  of  all  dip  pipes  leading  into  the  main 
y  =  the  total  cross- sectional  area  of  the  main,  and 

d  —  the  extent  to  which  the  dips  are  sealed  when  the  box  is  open  to  the 
atmosphere, 

then  the  total  back-pressure  which  the  pipes  will  withstand  before  letting  back  gas 
(neglecting  any  variation  in  density  of  the  liquid) 


Thus  with  a  £-inch  seal,  which  is  frequently  found  with  modern  methods  of  obtain- 
ing high  gas  "  makes,"  the  back-pressure  which  would  be  withstood  is  6  inches, 
on  the  assumption  that  the  respective  areas  x  and  y  are  as  1  to  12,  or  10  inches  if 
the  ratio  is  1  to  20.  At  the  time  when  this  function  of  the  hydraulic  main  was  con- 
ceived seals  were  commonly  so  much  as  3  inches  in  depth,  and  capable  of  with- 
standing a  back-pressure  of  30  inches. 

On  the  other  hand,  the  amount  of  "  draw  "  which  can  be  applied  to  the  main 
before  the  seal  is  broken  forwards  is  given  by  the  following  :  — 


Draw  "  must  not  exceed — 

x 


y  —  x 


X  d 


providing  that  no  overflow  for  the  liquor  is  employed.  That  is  to  say,  with  a 
1-inch  seal  the  vacuum  before  the  seal  is  overcome  may  equal  l^y  inch,  or  with  a 
f-inch  seal  0-54  inch,  again  assuming  a  ratio  of  areas  of  12  to  1.  But  on  all  systems 
of  hydraulic  mains  some  form  of  liquor  overflow,  whether  it  be  by  weir  valve  or 
tar  tower,  is  imperative ;  accordingly  the  above  formula  has  little  bearing  on  the 
conditions  of  seal  in  the  hydraulic  main.  If  a  permanent  overflow  is  provided,  then 
the  liquor  outside  the  dip  pipe  can  never  rise  above  a  certain  level ;  consequently, 
the  difference  in  level  of  the  liquid  in  and  outside  the  pipe  during  the  application 
of  a  vacuum  will  be  brought  about  solely  by  the  fall  in  level  of  the  liquid  inside 
the  pipe.  Hence,  if  a  vacuum  of  1-inch  is  applied  to  the  hydraulic,  the  liquid 
in  the  dip  pipe  will  fall  1  inch.  Consequently,,  before  the  seal  is  broken  a  "  draw  " 
equivalent  to  the  original  seal  can  be  applied. 


168  MODERN   GASWORKS   PRACTICE 

ANTI-DIPS  AND  DRY  MAINS 

Since  with  modern  methods  of  carbonization  there  is  frequently  a  vacuum  in 
the  ascension  pipe,  so  that  air  is  drawn  forward  when  the  retort  doors  are  open, 
and,  furthermore,  it  has  been  shown  that  the  safety-seal  function  of  the 
hydraulic  is,  with  light  seals,  practically  valueless,  there  is  strong  reason  to  suppose 
that  the  liquor  seal  could  be  dispensed  with  altogether.  In  order,  however,  that 
the  drawing-in  of  air,  with  its  consequent  deteriorating  effect  upon  the  quality  of 
the  gas,  may  be  precluded,  the  device  known  as  the  anti-dip  or  dry  main  has  been 
introduced.  Primarily,  it  consists  of  receptacle  similar  to  the  hydraulic  main,  but 
without  the  permanent  liquor  seal,  means  being  provided  for  closing  the  inlet  to 
the  main  during  the  time  when  the  retort  doors  are  open. 

The  chief  claims  which  can  be  made  for  the  dry  main  are  the  following : — 

(a)  The  liquor  (or  tar)  seal  is  abolished,  consequently  any  deterioration  which 
the  gas  may  suffer,  due  to  the  bubbling,  is  avoided. 

(6)  There  is  no  continuous  fluctuation  of  pressure  or  vacuum  in  the  ascension 
pipe,  and  consequently  in  the  retort.  In  fact,  oscillation  is  absent. 

(c)  No  air  is  pulled  in  during  the  time  the  retort  doors  are  open,  as  is  often  the 
case  with  the  hydraulic  seal. 

(d)  Little,  if  any,  pressure  in  hydraulic  main  and  retort,  therefore  less  scurf 
formed. 

(e)  If  the  main  gets  out  of  level  the  consequences  are  not  very  serious. 

On  the  other  hand,  the  appliance  for  making  and  breaking  the  seal  entails  the 
use  of  fairly  costly  apparatus,  which  increases  the  original  expenditure  and  the  wear 
and  tear. 

Anti-dips  now  in  use  may  be  classified  under  three  distinct  heads,  namely : — 

(a)  Those  where,  by  means  of  some  form  of  plug  or  valve,  the  free-way  in  the 
ascension  pipe  is  completely  closed.  This  may  be  done  by  a  butterfly  or  plug  valve 
in  the  arch  pipe,  or  by  closing  the  open  end  of  the  dip  pipe  by  means  of  a  movable 
plug. 

(6)  Types  in  which  the  liquor  is  raised  at  will,  so  as  to  seal  the  dip  pipes. 

(c)  Types  in  which  the  liquor  is  lowered  at  will  so  as  to  unseal  the  dip  pipes. 

The  earliest  forms  of  anti-dips  were  mainly  constructed  on  the  principle  of  the 
first  of  the  above,  one  such  being  illustrated  in  Fig.  125.  In  most  cases,  however, 
these  have  proved  more  or  less  unsatisfactory,  chiefly  owing  to  sticking  of  the 
plugs  or  valves  due  to  the  accumulation  of  tar,  or  to  the  imperfect  closing  of  the 
valves  so  that  they  are  not  gastight.  Modern  improvements  of  this  type  of  anti- 
dips  are  the  designs  introduced  by  Simmonds  and  Davidson  and  shown  in  Figs.  126 
and  127.  In  Davidson's  system  the  base  of  the  dip  pipe  is  machined  on  the  inside 
so  as  to  form  a  seating  for  the  cast-iron  cone  suspended  from  the  rod  passing  through 
a  stuffing  box  in  the  specially  designed  bridge  pipe.  The  cone  is  pulled  up  on  to  its 
seating  and  released  by  means  of  a  weighted  lever  arrangement  which  is  operated 
from  the  charging  floor.  The  stuffing  box  is  packed  with  greasy  packing.  The 
advantages  claimed  for  this  type  are  that  it  permits  of  continuous  draining  away  of 


RETORT-BENCH   APPURTENANCES 


169 


tar  and  liquor,  so  that  the  main  is  practically  empty,  and  it  does  not — as  is  the  case 
with  so  many  dry  mains — curtail  the  capacity  of  the  main,  or  involve  the  use  of 
•complicated  appliances  which  are  out  of  reach  during  working. 

In  Simmonds'  anti-dip  the  dip  pipe  is  sealed  in  liquor  in  the  usual  way,  and 


FIG.  125. — SIMPLE  THROTTLE- 
TYPE  ANTI-DIP. 


FIG.  126. — SIMMONDS'  ANTI-DIP. 


an  aperture  for  the  passage  of  the  gas  is  provided  in  the  side  of  the  pipe  above  the 
liquor  level.  At  this  point  a  square  valve  face  is  cast  on  to  the  side  of  the  pipe,  the 
area  of  the  gas  outlet  being  equivalent  to  the  cross-sectional  area  at  the  base  of  the 
pipe.  The  faced  slide  valve  is  operated  by  means  of  a  rod 
passing  through  a  stuffing-box  and  connected  to  a  counter- 
weighted  lever.  The  operating  handle  extends  to  the 
charging  floor,  being  held  down  during  the  period  of  gas 
making  so  that  the  seal  is  by-passed,  and  released  whilst 
the  retort  doors  are  open  in  order  to  prevent^he  intake  of 
air.  A  flange  is  provided  at  the  valve-rod  gland  which 
gives  sufficient  room  for  the  valve  to  be  withdrawn  when 
re-facing  is  necessary. 

.  The  same  principle  of  interposing  a  liquor  seal  is 
made  use  of  in  Cort's  anti-dip  (Fig.  128),  but  in  this  case 
a  double  dip  pipe  is  employed,  the  outer  pipe  being  in  the 
nature  of  a  sliding  sleeve.  When  the  retort  doors  are 
closed  the  sleeve  is  drawn  upwards  to  its  fullest  extent,  so 
that  the  gas  passes  direct  from  the  inner  pipe  to  the  foul 
main.  When  the  doors  are  opened  the  sleeve,  by  means  of 
suitable  gear,  is  dropped,  and  forms  a  liquor  seal  which  pre- 
cludes the  possibility  of  air  going  forward. 

Helps'    anti-dip     (Fig.    129)    is   unique   in   that   no 

mechanically  operated  appliance  is  entailed ;  hence  one  of  the  chief  difficulties  with 
dry  mains  is  avoided.     Attached  to  the  back  of  the  hydraulic  main,  and  running 


FIG.  127. — DAVIDSON'S 
ANTI-DIP. 


170 


MODERN   GASWORKS   PRACTICE 


FIG.  128. — CORT'S  ANTI-DIP. 

to  the  displacement  chamber, 
chamber,  with  a  corresponding 
rise  in  level  in  the  hydraulic, 
the  latter  rise  being  sufficient 
to  seal  the  dip  pipes,  thereby 
closing  the  free-way  of  the 
ascension  pipes.  The  differ- 
ence in  level  will,  of  course,  be 
the  same  as  the  difference  in 
pressure  of  the  pressure  gas 
used  and  the  vacuum  produced 
by  the  exhauster.  In  this 
system  it  will  be  noticed  that 
all  retorts  in  the  bench  are 
simultaneously  sealed,  whether 
their  doors  are  open  or  not.  A 
wheel  is  attached  to  the  three- 
way  valve,  and  the  change  is 
effected  by  a  chain  passing 
round  the  former  and  hanging 
down  to  the  stage  floor.  It  will 
be  seen  that  the  only  working 
part,  the  three-way  valve,  never 
comes  in  contact  with  the  new- 
ly made  gas  and  tarry  vapours. 


the  whole  length  of  the  main,  is  a  displacement 
chamber.  Communication  is  effected  between 
the  hydraulic  and  displacement  chamber  by 
means  of  the  small  pipes,  as  shown,  whilst  a. 
three-way  valve  has  two  of  its  ports  connected 
to  the  two  connecting  pipes  respectively,  and 
the  third  to  a  supply  of  gas  under  pressure,  taken 
back  (say)  from  the  mains  leaving  the  purifiers. 
The  displacement  chamber,,  by  a  turn  of  the 
three-way  valve,  is  accordingly  put  in  connexion, 
with  the  vacuum  exerted  on  the  hydraulic  by 
the  exhauster  or  with  the  pressure  in  the  mains 
beyond  the  purifiers.  The  level  of  liquor  m> 
the  hydraulic  is  set  so  as  to  give  a  clear  pas- 
sage through  the  dip  pipe ;  and,  when  the 
retort  doors  are  shut,  the  displacement  chamber 
is  under  a  similar  vacuum  to  that  prevailing 
in  the  hydraulic.  When  the  retort  doors  are 
opened,  however,  the  pressure  gas  is  admitted 
This  causes  a  depression  of  the  liquid  in  the 


To  Retort  Honse  Wall 
or  Other  Convenient  Plar.e 


Wheel  to  Operate 
Two-Way  Valve 

No.  1          No.  2 


Fie.  129. — HELPS'  ANTI-DIP. 


RETORT-BENCH   APPURTENANCES 


171 


TAKE-OFFS   FOR  TAR  AND  LIQUOR 


c 


For  many  years,  until  recently,  the  weir  valve  was  by  far  the  most  common 

method    in    use    for  disposing  of  the 

liquor  and  tar  from  the  hydraulic  main. 

As  before   explained,  the  gas,  liquor, 

and  tar  were  removed  through  a  com- 
mon outlet,  a  tar  shield  usually  being 

provided,   so    that   liquor  formed   the 

greater  part  of  the  liquid  remaining  in 

the  hydraulic.     The  three  products  of 

distillation  then  flowed  together  to  the 

foul  main,  from  the  bottom  of  which  the 

liquids  were  drawn  off  through  seals 

and  run  to    the  storage  wells,  where 

separation,  due  to  gravity,  took  place. 

In  spite  of  the  introduction  of  more 

effective  appliances,  the  weir  valve  is 

still  in  fairly  common  use,  and  forms  a 

ready  and  reliable  means  for  the  regu- 
lation of  seals.     The  construction    of 

the  valve  is    simple,  and  is  shown  in 

detail  in  Fig.  130. 

A  more  recent  means  for  the  dis- 
posal of  tar  and  liquor  is  that  intro- 
ducing the  principle  of  the  tar  box,  in 

which  the  gas  outlet  is  distinct  from 

that  of  the  liquids,  and  seal  regulation 

is  effected  by  the  height  of  overflow  of  the  latter.     The  principle  introduced  is  in 

reality  that  of  the  U-gauge,  one  limb  being  the 
hydraulic  main  and  the  other  limb  the  tar-overflow 
pipe.  The  arrangement  will  be  readily  understood  by 
reference  to  Fig.  131.  It  will  be  seen  that  the  tar- 
box  casting  is  attached  to  the  side  of  the  hydraulic, 
seal  regulation  being  effected  by  the  running  socket, 
as  shown.  Owing  to  the  greater  density  of  the  tar, 
the  height  of  the  liquid  level  in  the  tar  box  will  be 
slightly  below  that  of  the  liquor  in  the  hydraulic  main. 
An  important  feature  is  the  equilibrium  pipe  between 
the  tar  box  and  main,  which  ensures  the  same  con- 
ditions prevailing  above  the  two  columns  of  liquid. 
Tar  boxes  of  this  type  are,  at  the  present  day,  very 

seldom  erected,  as  they  are  not  always  reliable  in  their 
FIG.  131. — SHOWING  PRINCIPLE  .  ' .  J  J 

OF  ACTION  OF  TAR  Box.          action  and  entail  a  good  deal  of  attention.     They  are,. 


FIG.  130..— TYPICAL  WEIR  VALVE. 


Equilibrium  Pipe 


172 


MODERN   GASWORKS   PRACTICE 


Equilibrium 
Pipe 


moreover,  expensive  in  the  first  instance  ;  and  have  almost  wholly  given  way  to 
the  principle  of  the  Dillamore  tar  tower,  which  provides  an  extremely  simple 
.and  effective  means  for  both  the  regulation  of  seals  and  the  collection  of  tar 
and  liquor. 

TAR  TOWERS 

Probably  one  of  the  most  striking  features  of  present-day  retort-bench  equipment 
is  the  manner  in  which  the  Dillamore  tar  tower — an  appliance  originally  introduced 
many  years  ago,  but  with  mixed  results — has  forced  its  once- despised  merits  upon 

,  the  attention  of  the  gas   engineer, 

so  that  it  is  now  looked  upon  as 
furnishing  the  most  ideal  means  for 
seal  regulation  and  tar  and  liquor 
disposal.  It  may  be  said  that  each 
engineer  who  favours  tar  towers  has 
his  own  particular  way  of  fitting 
them  up ;  hence  no  hard-and-fast 
rules  can  be  laid  down.  In  general, 
however,  it  will  be  found  profitable 
to  aim  at  leaving  the  interior  of  the 
tower  as  unencumbered  with  pipe- 
work as  possible,  and  with  this  end 
in  view  the  author  suggests  the 
scheme  shown  in  Fig.  132  as  being 
the  least  costly  and  the  most  satis- 
factory from  the  standpoint  of  re- 
liability. The  merits  of  tower 
,  systems  are  too  well  known  to  need 

repetition  here.  The  more  common 
defects  which  may  go  unnoticed  for 
a  time  may  be  briefly  summarized  as 
follows : — 

(a)  In  many  cases  an  external 
or  internal  seal  is  employed,  so  that 
the  liquor  flow  from  the  box  may  be  readily  seen.  The  warm  liquor  flowing  out 
in  this  way  is  responsible  for  appreciable  ammonia  losses,  and  the  liquor  should 
preferably  be  led  to  a  closely  covered  seal-pot. 

(6)  Choked  or  partly  choked  equilibrium  pipes  may  go  unnoticed  for  some  time, 
with  the  result  that  the  seal  on  the  dip  pipes  is  not  what  it  is  thought  to  be. 

(c)  It  must  be  remembered  that  a  tar  tower  and  the  hydraulic  main,  connected 
together  by  the  tar  inflow  pipe,  in  reality  form  a  U-gauge,  and  the  weights  per  unit 
of  area  of  the  two  columns  balance  one  another.  Consequently,  fluctuations  in 
specific  gravity  in  the  liquid  in  the  two  columns  will  be  responsible  for  a  rise  or  fall 
in  level,  hence  alteration  of  the  seal.  Differences  in  temperature  are  also  followed 


FIG.  132. — AN  EFFECTIVE  TAB  TOWER  SCHEME. 


RETORT-BENCH  APPURTENANCES 


173 


iT'i  i        m> 

j    Seal  Regulator 

II 


Liquor  Level 


Open  to  Alt' 
to  prevent 
Syphoning 


Seal 


Liquor 
Overflow 


FIG.  133. — TOWER  WITH 
INTERNAL  SEAL. 


by  similar  effects.      It  has  been  shown  that  if  a  varia- 
tion of  30°  C.  occurs  in  the  temperatures  of  the  liquid 

in  the  tower  and  hydraulic  main  (for  instance,  if   the 

temperature  of  the  liquor  in  the  tower  rose  from  20°  C. 

to  30°  C.  and  that  of  the  liquor  in  the  hydraulic  main 

fell  from  70°  C.  to  60°  C.)  this  alone  maybe  responsible 

for  a  variation  of  4|-tenths  in  the   seal.     To  minimize 

this  effect  as  far  as  possible  it  is  advisable  to  connect 

the   main  tar  pipe  to  the  tower  as   high  up  as  can 

reasonably   be   done,   and  to  ensure  that  the  tower  is 

flushed  down  before  the  accumulated  tar  reaches  the 

level  of  this  pipe. 

(d)  A  special  means  should  be  provided  for  guard- 
ing against  the  possibility  of  unsealing  the  dip  pipes 

when  the  tower  is  discharged.     It  is  usual  to  run  liquor 

into  the  tower  whilst  the  tar  is  being  run  off ;  but  even 

under  such  conditions  the  outward  flow  may  be  greater 

than  the  inward  flow,  thus  the  level  will  fall.     A  simple 

means  of  seeing  at  a  glance  whether  or  not  the  seal  is  being  maintained  is  to  fit  a 

|-inch  test  pipe,  as  shown  in  Fig.  132.  When 
the  tower  is  flushed  the  ^-inch  test  cock  is 
opened,  and  so  long  as  liquor  passes  down 
this  pipe  a  seal  is  ensured. 

(e)  The  only  questionable  drawback  to  the 
liquor  take-off  from  the  tower  as  shown  in 
Fig.  132  is  the  possibility  that  the  outlet  pipe 
may  become  choked,  and,  owing  to  the  liquor 
flowing  into  a  covered  seal  pot  the  stoppage 
may  not  be  immediately  noticed.  In  this  case 
the  tower  gradually  fills,  with  the  result  that 
a  heavy  seal  is  thrown  upon  all  the  dip  pipes. 
It  is  scarcely  necessary  to  mention  that  on  all 
installations  of  the  kind,  bends  in  the  pipe 
work  should  be  rigidly  avoided,  and  plugged 
crosses  should  be  used  wherever  possible. 

(/)  It  is  always  advisable  to  provide  for  a 
constant  trickle  of  liquor  when  towers  are  in 
use.  Although  this  is  frequently  admitted  at 
the  hydraulic  main,  it  is  far  preferable  to 
arrange  for  the  supply  direct  to  the  tower — 
the  latter  being  cooler,  there  is  less  likelihood 
of  ammonia  loss. 

(a)  In  cases  where  outside  or  inside  seal- 
-TOWER  WITH    EXTERNAL       . 

SEAL  ing  arrangements  are  provided,  care  must  be- 


FIG.    134.- 


174 


MODERN   GASWORKS   PRACTICE 


I  Running  Socket 


taken  to  ensure  that  all  possibility  of  syphoning  is  avoided.  To  this  end,  some 
portion  of  the  pipework  must  be  open  to  the  atmosphere,  whilst  it  will  be  noticed 
that  in  the  system  shown  in  Fig.  132  this  is  not  necessary,  as  syphoning  could  not 
take  place. 

Sketches  of  the  outside  and  inside  seal  types  are  given  in  Figs.  133  and  134,  and 
the  anti-syphon  precautions  will  be  noted.  A  decidedly  uncommon  and  novel  arrange- 
ment is  that  shown  in  Fig.  135.  In  this  instance  the  depth  of  seal  on  the  dip  pipes 
is  entirely  governed  by  the  constant  overflow  of  tar,  the  outlet  pipe  for  the  latter 
being  brought  up  from  the  base  of  the  tower  to  a  point  on  about  a  level  with  the 
bottom  of  the  hydraulic  mains.  Accordingly,  it  is  tar,  and  not  liquor,  which  is 

constantly  trickling  away  ;  and 
since  more  liquor  than  tar  is 
formed,  a  special  draw-off  cock  for 
the  former  is  provided  about  two- 
thirds  of  the  way  up  the  tower, 
and  a  certain  amount  of  liquor  is 
daily  run  off  so  as  to  ensure  there 
always  being  tar  at  the  bottom  of 
the  tower.  The  chief  advantage 
claimed  is  that  the  liquor  may  be 
worked  up  to  greater  strength  than 
is  the  case  with  the  more  ordinary 
tower  systems,  whilst  there  is  no 
constant  stream  of  warm  liquor 
running  away  to  the  wells. 

An  uncommon  idea,  infre- 
quently met  with,  is  that  shown  in 
Figs.  136  and  137.  It  consists  of 
combining  the  usually  distinct 
apparatus  of  tar-tower  and  retort- 
house  governor.  The  tower  is 
made  considerably  higher  than  is 
general,  and  the  upper  portion 
contains  a  special  receptacle  which 

takes  a  floating  bell  of  greater  diameter  than  the  tower  proper.  The  bell  chamber 
is  closed  by  a  cover  plate  having  a  centrally  disposed  hole  through  which  a  rod 
passes,  by  means  of  which  the  governor  may  be  adjusted.  Immediately  below  the 
bell  chamber  is  the  gas  inlet.  The  subsequent  passage  of  the  gas  may  be  seen 
from  the  section  given  in  Fig.  137.  The  governor  valve  serves  to  throttle  the 
passage  of  the  gas  should  the  vacuum  increase  above  the  normal,  while,  should 
the  vacuum  decrease,  the  valve  is  raised,  with  a  consequent  increase  in  the  area 
of  the  gas  passage,  due  to  the  increase  in  pressure  of  the  gas  on  the  bell. 

During  the  last  few  years  there  has  been  a  growing  tendency  to  erect  tar  towers 
built  up  from  mild  steel  plates  and  sections.  It  is  somewhat  difficult  to  understand 


Tar  Overflow 
to  Well 


Tar  Flu»h  Cock 


FIG.  135. — SEAL  REGULATION  BY  TAB  OVERFLOW. 


RETORT-BENCH  APPURTENANCES 


175 


why  this  should  be  done,  for  the  ordinary  cast-iron  pipe  cannot  be  excelled,  and  is 
•extremely  cheap.  Possibly,  the  steel  tower  was  originally  introduced  owing  to  the 
objection  to  sending  cast-iron  work  long  distances,  when  it  is  liable  to  rough 
handling  and  damage. 

The  experience  of  Mr.  J.  G.  Newbigging  in  connexion  with  ammonia  losses 
may  be  mentioned,  as  bearing  out  the  arguments  that 
the  internal  or  external  seals  with  tar  towers  are  un- 
necessary and  actually  wasteful,  and  that  it  is  far  prefer- 
able to  take  the  liquor  direct  to  an  effectively  sealed  pot. 
It  had  been  Mr.  Newbigging's  general  custom  to  ran  liquor 
into  his  mains  from  an  over- 
head tank,  when  striking 
differences  in  the  amount  of 
free  and  fixed  ammonia  led 
him  to  make  investigations. 
Two  deductions  were  made, 
the  first  being  that  ammonia  - 
cal  liquor  constantly  overflow- 
ing the  weir  valves  was  in  such 
a  state  that  free  ammonia  was 
being  driven  off  in  large  quan- 
tities, and,  consequently,  any 
FIG.  '136. — COMBINED  TAB 

HOUSE  GOVERNOR.          rent  in  the  pipe  line  or  to  the 
atmosphere  meant  a  probable 

source  of  serious  loss.  To  overcome  such  drawbacks,  water,  instead  of  liquor, 
was  used  for  flushing  the  hydraulic  mains,  and  in  this  manner  ammonia  loss  was 
curtailed,  owing,  it  is  said,  to  a  lower  percentage  of  free  ammonia  in  the  liquor 
overflowing  the  weir  valves.  In  view  of  these  results,  it  might  appear  advisable 
to  admit  water  instead  of  the  usual  trickle  of  liquor  to  the  hydraulic  mains,  but 
the  author  considers  the  practice  undesirable. 

THE   PITCHING-UP   OF  MAINS,    ETC. 

The  pipes  which  are  used  for  conveying  the  tar  and  liquor  from  the  hydraulic 
mains  to  the  storage  well  are  often  a  source  of  trouble  owing  to  the  adherence  of 
pitchy  matter  to  the  inside,  thereby  causing  blockage.  This  is  particularly  the  case 
where  the  pipes  are  subjected  to  radiated  heat  from  the  retort  bench.  The  most 
effective  means  of  collecting  liquor,  and  at  the  same  time  furnishing  a  flushing  system 
for  the  draw-off  pipes  and  hydraulic,  is  to  provide  a  tank  into  which  all  liquor  running 
from  the  foul  main,  hydraulic  mains,  or  tar  towers,  is  taken.  This  liquor  is  then  raised 
by  means  of  a  pump  to  an  upper  tank  a  few  feefrabove  the  retort  bench,  and  provides 
the  constant  feed  to  the  tar  towers  as  already  explained.  The  chief  function  of  the 
pump,  however,  is  that  of  periodically  flushing  out  the  tar  pipes.  This  is  effected 
by  fitting  a  connexion  from  the  delivery  of  the  pump  to  the  run-off  pipes  of  each 


TOWER  AND    RETORT    exposure  to  either  an  air  cur-  FIG.  _  i37.-fl.cnoK   OF    COM- 


176 


MODERN   GASWORKS   PRACTICE 


individual  tar-tower  system.  Accordingly  a  flush  of  liquor  at  considerable  pressure 
can  be  pumped  backwards  through  the  pipes  and  into  the  hydraulics.  A  short 
period  of  such  flushing  carried  out  once  a  day,  or  even  once  during  each  shift,  pre- 
cludes the  possibility  of  stoppage.  The  system  of  liquor  tanks,  moreover,  has  other 
advantages,  in  that  the  warm  liquor  coming  straight  from  the  towers  and  foul  main 
is  permitted  time  to  cool  down  before  being  discharged  into  the  storage  well,  thus 
curtailing  loss  of  ammonia.  A  further  advantage  is  that  the  liquor  run  into  the 
towers  or  mains  can  be  kept  in  continuous  circulation  (only  the  surplus  being  allowed 
to  drain  off  to  the  well  through  an  overflow  in  the  lower  tank),  which  results  in  a 
greatly  increased  strength  being  obtained.  When  liquor  is  circulated  in  this  manner 

TAB  AND  WATER 
FEED  TO  MAIN 


EQUILIBRIUM  PIPE 


ADJUSTABLE 
SOCKET 


AS  MAIN 


CHLORIDE  WATER 
TAR 


FIG.  138. — SMITH  &  PEARSON'S  ARRANGEMENT  FOR  ABSORBING  AMMONIUM  CHLORIDE. 


it  will  usually  be  found  that  the  proportion  of  "  fixed  "  ammonia  is  appreciably 
greater  than  when  ordinary  methods  are  employed. 

Smith  and  Pearson,  in  the  course  of  their  researches  carried  out  with  the  Birming- 
ham coal-testing  plant,  found  that,  so  far  as  the  pitchy  deposits  in  the  hydraulic  main 
were  concerned,  the  chief  binding  material  in  the  pitch  appeared  to  be  ammonium 
chloride  taken  up  from  the  gas  in  the  hydraulic  main.  In  order  to  eliminate  this 
effect,  they  absorbed  the  chloride  before  it  could  reach  the  tar  by  interposing  a  layer 
of  water,  3  inches  deep,  on  top  of  the  tar.  The  water  was  run  in  hot,  so  that  little 
free  ammonia  was  taken  up,  and  the  chloride  in  the  gas  was  reduced.  Considerable 
benefit  resulted  from  the  arrangement,  which  is  diagrammatically  illustrated  in 
Fig.  138. 

HYDRAULIC  MAIN  AGITATORS 

Where  modern  methods  for  the  drawing-off  of  tar  and  the  flushing  of  hydraulic 
mains  are  in  use,  little  trouble  is  experienced  from  stoppage  and  erratic  working 
due  to  "  pitching- up."  The  disorganization  resulting  from  the  latter,  however, 
has  in  some  cases  been  sufficiently  severe  to  warrant  the  use  of  special  agitating 
devices. 

A  common  type  of  apparatus  for  the  purpose  is  illustrated  in  Fig.  139.     It  con- 


RETORT-BENCH   APPURTENANCES 


177 


sists  of  an  endless  chain  passing  over  two  sprocket  wheels,  situated  one  towards"each 
end  of  the  hydraulic  main.  Projecting  arms  or  scrapers  are  attached  to  the  chain, 
which  is  so  arranged  that  the  underside  drags  along  the  floor  of  the  main.  By  means 
of  a  projecting  spindle  the  chain  can  be  set  in  motion  at  periodical  intervals.  Needless 
to  say,  it  is  strongly  inadvisable  to 
encumber  the  hydraulic  with  appara- 
tus of  this  type  when  it  can  possibly 
be  avoided.  If  flushing  or  agitation 
is  desired,  it  should  be  carried  out  by 
liquid  and  not  mechanical  means. 

Modern  hydraulic  mains  all  tend 
to  be  somewhat  smaller  and  more 
shallow  than  many  of  the  old  cast- 


iron  types.    The  tendency  is  certainly 
to  be  encouraged,  for  the  function  of 

the  hydraulic  is  not  that  of  a  storage 

J  f  T  FIG.  139. — HYDRAULIC  MAIN  AGITATOR. 

tank,  and  the  depth  of  liquor  should 

be  as  shallow  as  possible,  providing  that  it  satisfactorily  performs  its  primary 
duty  of  ensuring  a  seal.  If  a  considerable  volume  of  liquid  is  always  allowed  to 
remain  in  the  hydraulic,  there  is  a  tendency  for  distillation  to  take  place ;  and,  as 
tar  will  inevitably  settle  out,  the  formation  of  pitch  is  only  a  matter  of  time,  unless 
special  precautions  are  taken  to  keep  it  down. 

THE  FOUL  MAIN 

The  foul  main  may  be  called  upon  to  perform  more  duties  than  one,  and  amongst 
other  functions  it  provides  : — 

(a)  A  gas  conduit  between  carbonization  and  primary  purification  plant. 

(6)  A  drain  pipe  for  liquor  and  tar. 

(c)  A  primary  condenser. 

So  far  as  the  last  duty  is  concerned,  the  total  length  of  foul  main  should  be 
included  when  calculations  for  condensing  capacity  are  made. 

The  size  of  the  foul  main  must  depend  upon  the  combined  areas  of  all  pipes 
leading  into  it.  Theoretically,  the  cross- sectional  area  should  be  equivalent  to  the 
sum  of  the  areas  of  the  latter  pipes,  but  this  is  never  carried  out  in  practice,  first 
because  mains  of  such  capacity  are  unnecessary  owing  to  the  condensation  rapidly 
taking  place,  and  because  the  foul  main  is  delivering  gas  more  or  less  continuously, 
whereas  there  is  a  sudden  rush  of  gas  into  each  hydraulic  main  as  charging  takes  place. 

Generally  speaking,  the  following  sizes  for  foul  mains  are  those  prevailing,  and 
may  be  safely  applied:— 

CAPACITY  OF  BENCH  PER  SIZE  OP  FOUL  MAIN. 


24  HOURS.  If  one. 

(a)  30,000  to  100,000  cubic  feet 6  inches  to  9  inches. 

(6)  200,000  to  500,000  cubic  feet 12  inches  to  15  inches. 

(c)  1  million  to  If  million  cubic  feet    .'     .      .      .  18  inches. 

(d)  2  million  to  3  million  cubic  feet    .  24  inches. 


If  two. 


14  inches. 
18  inches. 

N 


FlG'  1°~ 


178  MODERN   GASWORKS   PRACTICE 

Another  rule  is  to  make  the  foul  main  (if  it  delivers  all  the  gas)  of  125  per  cent. 
the  area  of  the  main  connexions  in  the  works. 

Retort  benches  in  the  past  were  invariably  supplied  with  a  cast-iron  foul  main, 
but  the  modern  practice  is  to  construct  the  latter  from  lap-welded  steel  plates  or 
'solid  drawn  tubes.  When  the  foul  main  is  of  greater  diameter  than  12  inches,  steel 
should,  as  a  general  rule,  be  used,  and  in  such  cases  it  will  usually  be  slightly  cheaper 
than  cast-iron.  A  further  recommendation  is  that  owing  to  the  thinner  metal  walls 
employed  in  the  steel  pipe  the  outward  radiation  of  heat  is  greater,  hence  the  cooling 
effect  on  the  gas  is  very  much  more  pronounced. 

As  the  foul  main  is  situated  above  the  retort  bench  it  is  liable  to  undergo  con- 
siderable expansion  when  the  heats  are  raised  ready  for  work  ;  accordingly  some 
means  must  be  introduced  for  the  prevention  of  breakage. 
With  the  cast-iron  main,  the  lead  joints  at  the  spigots 
will  be  sufficient  to  cope  with  any  change  of  length,  and 
flange  joints  should,  therefore,  be  avoided,  unless  some 
form  of  expansion  joint  is  inserted. 

The  steel  foul  main,  having  no  flexible  joints  to  yield 
to  movement,  should  —  if  of  any  length  —  always  be  pro- 
vided with  an  expansion  joint  similar  to  that  shown  in  Fig. 

14°-  In  the  usual  way  one  of  these  i°ints  win  be  necessary 

for  each  100  feet  of  pipe.     In  modern  work  the  foul  main 
is  usually  supported  on  the  cross-stays,  or  from  them  by  chains  or  steel  straps. 

RETORT-HOUSE   GOVERNORS 

The  retort-house  governor  is  an  auxiliary,  more  or  less  essential  in  the  larger 
works,  of  comparatively  recent  introduction.  It  differs  from  the  ordinary  station 
type  of  governor  (which  forms  the  last  piece  of  apparatus  through  which  the  gas 
passes  before  leaving  the  works)  in  that  whilst  the  latter  is  employed  with  the  object 
of  reducing  pressure,  the  retort-house  governor  is  interposed  for  the  purpose  of 
reducing  the  intensity  of  vacuum  created  by  the  exhauster.  This,  however,  is  not 
its  primary  function.  In  the  same  way  that  the  station  governor  ensures  a 
steadiness  of  pressure  in  the  consumers'  services,  whatever  may  be  the  demand,  so 
should  the  retort-  house  governor  ensure  a  constant  vacuum  in  the  hydraulic  main, 
whatever  the  volume  of  gas  coming  away  from  the  coal  charges.  The  intensity  of 
vacuum  desired  is  obtained  by  means  of  "loading  "  on  similar  lines  to  the  method 
prevailing  with  station  governors. 

Before  the  introduction  of  this  apparatus  the  required  vacuum  on  the  foul  main 
was  obtained  by  regulation  of  the  speed  of  the  exhauster  ;  whereas  the  uniformity 
of  the  "  draw  "  was  controlled  as  effectively  as  possible,  but  not  without  considerable 
difficulty,  by  means  of  the  ordinary  type  of  exhauster-governor  working  on  the 
throttle  of  the  engine  or  a  by-pass.  (For  description,  see  Chap.  XIII.)  This  method 
of  regulation  is  still  in  vogue  in  those  works  where  no  retort-house  governor  is  installed. 

The  application  of  the  retort-  house  governor  requires  some  consideration  in 
relation  to  the  working  of  horizontal  settings,  owing  to  the  operation  of  gas  making 


RETORT-BENCH   APPURTENANCES 


179 


being  necessarily  intermittent,  and  to  the  impracticability  of  charging  the  whole 
bench  of  retorts  at  the  same  moment.  For  instance,  if  a  single  retort  bench,  working 
into  a  common  hydraulic  main,  is  considered,  it  will  be  seen  that,  owing  to  the  different 
periods  at  which  the  distinct  rows  of  retorts  have  been  charged,  there  will  be  a  large 
volume  of  gas  coming  away  from  some  dip  pipes,  whereas  those  retorts  in  which  the 
charges  are  nearly  spent  will  be  yielding  little  or  no  gas.  But  the  object  of  the 
retort-house  governor  being  to  maintain  a  constant  "  pull "  whatever  the  quantity 
of  gas  coming  away  (and  providing  all  dip  pipes  are  equally  sealed),  there  will  be  a 
similar  vacuum  on  each  retort ;  that  is  to  say,  there  is  every  likelihood  of  drawing 
furnace  gases  up  the  pipes  from  those  retorts  where  the  charge  is  spent.  Under 
the  circumstances,  the  ideal  would  be  to  charge  up  an  entire  set,  or  series  of 
settings,  at  one  time  (instead  of  carrying  out  the  ordinary  practice  of  travelling  through 
the  whole  length  of  the  bench  on  a  definite  row  of  retorts),  and  to  interpose  a  retort- 
house  governor  for  each  unit  so  worked.  The  vacuum  could  then  be  gradually 
reduced  as  the  period  of  carbonization  on  each  distinct  section  advanced.  Such 
procedure,  however,  is  scarcely  possible  in  practice  ;  and  would,  moreover,  be  some- 
what antagonistic  to  the  purpose  in  view  of  those  engineers  with  a  penchant  for  high 
makes  per  ton. 

Owing  to  the  fact  that  the  retort- house '  governor  works  in  connexion  with  a 
system  of  mains  under  a  vacuum,  the  holder  bell — or  other  reservoir — in  communi- 
cation with  the  main  receives  no  support  from  the  gas,  consequently  buoyancy 
has  to  be  imparted  to  it  by  other  means.  In  general,  these  governors  may  be  divided 
into  two  groups,  namely — 

(a)  those  deriving  their  buoyancy  from  a  system  of  air  floats  within  the  holder 
bell,  and  being  regulated  by  direct  loading  of  the  latter ; 

(6)  those  in  which  no  air  floats  are  employed,  but  which  are  rendered  buoyant 
by  a  counterbalance. 

Both  types  are  in  common  use,  but  (6)  is  probably  preferable,  owing  to  the  tendency 
of  the  float  casings  to  cor- 
rode. The  arrangement  of 
the  air  chambers  is  shown 
in  Fig.  141,  and  it  may  be 
pointed  out  that  for  retort- 
house  governors  this  is  pre- 
ferable to  fixing  the  floats 
with  an  exterior  annular 
space  as  in  Fig.  142.  With 


Ain  Float 


Valve  Rod 


FIG.  141. 


FIG.  142. 


the  latter  arrangement  the 
governor   frequently    oper- 
ates   in   too    "  lively  "  a   manner  for  the   best  results.     On  the  other  hand,  for 
exhauster  governors,  the  annular  chamber  is  preferable. 

The  best  place  for  the  governor  is  on  top  of  the  retort  bench,  and  as  close  up  to 
the  end  of  each  section  of  the  foul  main  as  possible.     It  is  not  so  sensitive  when  fixed 


180 


MODERN   GASWORKS   PRACTICE 


FIG.  143. — ARRANGEMENT  OF  FOUL  MAINS  AND  RETOBT-HOTTSE  GOVERNORS  FOR  LARGE  BENCH. 
NOTE. — VALVES  (NOT  SHOWN)  ARE  REQUIRED  AT  THE  BASE  OF  EACH  GOVERNOR. 

on  the  inlet  or  outlet  of  the  condensers,  as  sometimes  found.  In  a  retort  house  of 
any  size,  more  than  one  governor  is  necessary,  and  the  different  sections  of  foul  main 
will  best  be  controlled  by  some  arrangement  as  that  shown  in  Fig.  143.  By-passes 
are  advisable  whenever  they  can  be  arranged  for,  as  the  governors  will  usually  require 
attention  about  every  four  months,  when  both  tank  and  valve  should  be  cleaned. 
A  typical  governor  of  the  counterbalanced  bell  type,  designed  on  Parkinson 
and  Cowan's  system,  is  illustrated  in  Fig.  144.  The  passage  of  the  gas  along  the  foul 

main  is  governed  by  the  sliding  reel 
which  depends  from  the  centre  of  the 
governor  bell.  At  the  same  time  com- 
munication between  the  holder  and  the 
main  on  the  retort-bench  side  is  effected 
by  the  service  pipe  shown.  By  means 
of  the  weights  the  bell  is  so  poised  that 
the  desired  vacuum  is  obtained.  Should 
the  gas  coming  from  the  retort  bench 
increase  in  volume,  then  the  vacuum  in 
the  foul  main  will  decrease,  with  the 
result  that  there  is  less  "  sucking-down  " 
on  the  bell,  which  accordingly  rises. 
This  movement  raises  the  reel  and  opens 
the  gas- way  until  the  previous  conditions 
of  vacuum  are  regained,  and  vice  versa. 
This  type  of  regulation,  with  the  open 
reel,  is  to  be  preferred  to  those  governors 
in  which  the  gas  in  its  tarry  condition  is 
forced  to  travel  through  narrow  slots. 
These  slots  lend  themselves  to  blockage, 
FIG.  144 .—RETORT-HOUSE  GOVERNOR.  particularly  when  a  system  of  dry  mains 


RETORT-BENCH   APPURTENANCES 


181 


FIG.  145. — "RBESON"   GOVERNOR  WITH  WATER 
LOADING  ATTACHMENT. 


Retort  House 
Governor 


is  in  use.  It  is  as  well  to  arrange 
for  a  thin  layer  of  oil  on  the  sur- 
face of  the  holder  water. 

A  new  departure  from  the 
ordinary  apparatus  is  the  "  Ree- 
son  "  governor,  shown  in  Fig.  145. 
In  this  apparatus  the  gasholder 
principle  is  done  away  with,  and 
its  place  is  taken  by  a  small 
flexible  reservoir  formed  by  a 
leather  diaphragm.  This  dia- 
phragm, being  in  direct  communi- 
cation with  the  foul  main,  is 

caused  to  collapse  or  distend  in  accordance  with  the  volume  of  gas  passing  along  the 
main.  The  movement  of  the  diaphragm  then  operates  the  butterfly  valve  and 
increases  or  diminishes  the  free  gas-way.  In  this  case  a  water-loading  attachment  for 
regulating  the  intensity  of  the  vacuum  is  shown.  The  chief  merits  of  the  governor 
are  its  compactness  and  the  small  possibility  offered  for  deterioration  by  corrosion. 

For  the  purpose  of  regula- 
tion, many  medium-sized  works 
employ  an  ordinary  butterfly 
valve  operated  from  a  bell. 

A  novel  hydraulic  main 
and  gas  take-off  arrangement 
has  been  introduced  by  Lang- 
ford.  This  is  shown  in  Fig.  146. 
It  will  be  seen  that  the  gas  is 
taken  off  from  the  top  of  the 
hydraulic,  whilst  the  liquor 
overflows  by  the  weir  valve 
attached  to  the  tower  and 
maintains  the  seal.  Originally, 
both  gas  and  liquor  were  re- 
moved in  the  ordinary  way  via 
the  weir  valve  on  the  hydraulic, 
but  excessive  oscillation  of  the 
liquor  occurred,  which  was  par- 
ticularly objectionable,  owing 
to  the  peculiar  type  of  ascension  and  dip  pipes,  unsealing  frequently  occurring. 
With  the  gas  outlet  moved  to  the  top  of  the  hydraulic,  the  vacuum  from  the  ex- 
hauster was  exerted  at  right  angles  to  the  surface  of  the  liquid,  thus  oscillation  was 
considerably  curtailed.  The  disposition  of  the  retort-house  governor  will  also  be 
noticed,  whilst  a  further  uncommon  practice  is  that  of  leading  the  carburetted 
water  gas  direct  to  the  hydraulic  main,  where  it  is  intermixed  with  the  coal  gas. 


FIG.  146. — LANGFORD'S  GOVERNOR  AND  TOWER  ARRANGE- 
MENT. 


CHAPTER   VIII 
THE   MECHANICAL   HANDLING   OF   MATERIALS 

THE  application  of  machinery  to  the  handling  of  all  types  of  gasworks  material 
has  during  recent  years  undergone  considerable  extension,  so  that,  nowadays,  even 
establishments  of  a  comparatively  small  order  can  instal  certain  types  of  labour- 
saving  plant  to  advantage.  Moreover,  recent  incidents  in  the  labour  world  and 
the  perfecting  of  the  more  or  less  crude  apparatus  of  former  years  has  added  a  certain 
stimulus  to  the  introduction  of  mechanical  means  for  performing  a  host  of  duties 
originally  carried  out  by  hand.  The  result  is  that  whereas  in  1893-7  about  twenty 
men  were  required  to  produce  a  million  cubic  feet  of  gas  per  diem,  to-day,  in  large 
installations  of  vertical  retorts,  the  number  is  only  four.  Roughly  speaking,  it 
may  be  taken  that  the  saving  of  a  single  man's  wages  warrants  a  capital  outlay  of 
between  £500  and  £600  on  machinery.  When  deciding  upon  the  question  of  the 
introduction  of  mechanical  plant,  however,  considerable  thought  is  necessary,  so 
that  the  various  charges  and  contra  charges  are  correctly  balanced  the  one  against 
the  other. 

The  principal  considerations  which  each  engineer  must  apply  to  the  case  in 
question  may  be  briefly  enumerated  as  follows : — 

(1)  Can  the  working  costs  be  curtailed,  and  if  so,  what  will  be  the  annual  saving  ? 

(2)  Will  better  carbonizing  results  follow  the  introduction  of  machinery,  and 
will  more  gas  be  obtained  from  the  plant  used  and  land  occupied.     If  so,  what 
will  be  the  effect  on  the  wear  and  tear  of  plant  ? 

(3)  Is  the  saving  represented  by  (1)  and  (2)  likely  to  be  sufficient  to  meet  the 
standing  charges  for  interest  on  capital  expenditure,  depreciation  and  repairs  ? 

(4)  Will  efficiency  be  sacrificed  in  order  to  effect  the  apparent  economy  ?      Loss 
of  efficiency  may  mean  losses  in  other  directions. 

(5)  Will  the  reduction  of  labour  relieve  the  management  of  any  difficulties  not 
actually  measurable  in  terms  of  £  s.  d.  ? 

When  the  works  is  of  any  magnitude  it  will  be  found  that  all  these  conditions 
can  be  replied  to  in  the  affirmative,  particularly  when  it  is  a  matter  of  conveying 
material  from  one  point  to  another,  or  from  a  low  level  to  a  higher  level. 

As  a  matter  of  fact,  retort-house  machinery  is  not  profitably  employed  in  small 
works,  although  those  manufacturing  20  million  cubic  feet  or  over  per  annum  can 
to  advantage  instal  such  types  as  the  "  Rapid  "  or  "  Manual "  machines,  which 
require  no  mechanical  power,  and  which  may  be  classed  as  labour-saving  devices 
though  not  necessarily  causing  much  diminution  in  expenses. 

182 


THE   MECHANICAL   HANDLING   OF   MATERIALS    183 

9 

As  an  example  of  the  economy  in  labour  to  be  effected  on  larger  works,  the 
case  of  the  500  million  works  considered  in  Chapter  I  may  be  taken.  The  coal 
gas  made  per  diem  in  this  instance  amounts  to  1,800,000  cubic  feet,  and  the  total 
outlay  involved  in  elevators,  conveyors,  coal  breakers,  charging  machinery,  and 
coke-handling  plant  is  given  as  £7,250.  Allowing  the  normal  figures  of  5  per  cent, 
for  interest  on  capital,  3  to  4  per  cent,  for  maintenance,  and  7|  per  cent,  for  depre- 
ciation (i.e.  a  total  of  16  per  cent.),  the  annual  saving  which  must  be  effected  is 
£1,160.  This  means  a  reduction  in  numbers  of  about  13  or  14  men,  or  (say)  4  or 
5  men  from  each  shift  per  day.  About  35,000  tons  of  coal  per  annum  would  be 
handled,  which  means  that  a  saving  of  8d.  per  ton  is  necessary  to  meet  the  above 
expenditure.  Accordingly,  those  in  authority  would  have  to  be  positively  assured 
that  such  a  saving  would  follow  the  introduction  of  machinery.  On  the  works 
in  question  there  is  little  doubt  that  this  economy — amounting  to  about  0-7d. 
per  1,000  cubic  feet  of  gas  produced — could  be  effected. 

Labour-saving  machinery  may  be  applied  on  gasworks  for  the  following 
purposes  : — 

(a)  The  charging  and  discharging  of  retorts. 

(6)  The  conveyance  of  coal  from  point  of  delivery  to  point  of  consumption. 

(c)  The  breaking  up  of  coal  to  the  required  size. 

(d)  The  conveyance  of  coke  from  the  retorts  to  a  suitable  storage  place,  or  to 
other  machinery  for  grading,  screening,  or  washing. 

(e)  Labour-saving  appliances  in  the  retort  house,  such  as  mechanical  pokers 
and  clinkerers. 

The  mechanical  handling  machinery  introduced  in  gasworks  is  almost  solely 
used  in  connexion  with  the  retort  house,  although  on  larger  works  other  raw  materials 
or  by-products,  such  as  oxide  of  iron  or  sulphate  of  ammonia,  may  be  profitably  dealt 
with  in  this  manner.  In  fact,  in  any  instance  where  a  saving  can  be  shown,  after 
consideration  on  lines  such  as  those  already  indicated,  the  instalment  of  machinery 
is  justified. 

CHARGING  AND  DISCHARGING  MACHINERY  FOR   RETORTS 

The  past  decade  has  witnessed  a  striking  change  in  the  design  of  machinery 
used  for  the  filling  and  emptying  of  horizontal  retorts.  The  introduction  of  the 
heavy  charge  and  the  mass  system  of  carbonization  has  been  responsible  for  much 
of  this  modification,  so  that  discharging  apparatus  embodying  the  principle  of  the 
rake — at  one  time  a  very  common  type — has  almost  entirely  disappeared.  This  is 
due  to  the  necessity  for  leaving  a  considerable  space  above  the  charge  in  the  retort 
in  which  the  rake  head  may  travel. 

Stoking  machinery  employed  in  operating  the  retorts  may  be  primarily  classified 
under  the  following  headings  : — 

1.  Machines  designed  to  minimize  the  labour  of  charging  or  discharging  but 
which  require  no  power  other  than  manual  labour  for  their  operation. 

2.  Machines  charging  simultaneously  from  both  sides  of  the  bench,  such  as  the 


184  MODERN   GASWORKS   PRACTICE 

Arroi-Foulis,  or  West's  scoop  charger.     These  types  of  machines,  though  still  at 
mse  in  many  instances,  are  scarcely  consistent  with  modern  requirements. 

3.  Machines  discharging  from  both  sides  of  the  bench  simultaneously.     These 
include  those  types  worked  on  the  rake  principle,  and  which  are  not  suitable  for 
heavy  charges. 

4.  Machines  charging  from  one  side  of  the  bench  only. 

(a)  Projectors. 

(6)  Those  embodying  the  principle  of  the  conveyor  chain. 

5.  Machines  discharging  from  one  side  only.     These  are  exclusively  worked 
on  the  principle  of  the  pusher. 

6.  Discharging  chargers,  which  simultaneously  empty  and  refill  the  retort. 

The  last-named  type,  though  not  altogether  satisfactory  at  the  time  of  its  intro- 
duction, is  now  reaching  a  stage  of  perfection  which  has  resulted  in  its  more  general 
adoption.  One  of  the  chief  disadvantages  attending  the  use  of  the  earlier  types 
was  the  impossibility  of  working  heavy  charges,  owing  to  the  necessity  for  leaving 
the  upper  portion  of  the  retort  clear  for  the  return  of  the  conveyor  chain.  This 
difficulty  has  now,  however,  been  surmounted. 

It  would  not  be  possible  to  describe  fully  here  the  details  of  construction  of 
all  the  machines  now  in  operation  in  gasworks  for  filling  and  discharging  retorts. 
It  is  merely  proposed  to  consider  the  most  familiar  examples,  and  to  indicate  briefly 
the  principles  upon  which  they  operate. 

The  engineer  who  is  contemplating  the  introduction  of  machinery  should  decide 
on  the  type  of  plant,  in  conjunction  with  the  apparatus  for  conveying  coal,  before 
proceeding  with  the  design  of  the  buildings  and  retort  plant.  Many  makers  have 
different  types  of  machinery,  such  as  those  with  or  without  storage  hoppers,  measur- 
ing chambers,  etc.  It  will,  therefore,  be  found  advantageous  to  settle  upon  the 
type  and  make  at  the  outset.  Once  the  machine  is  decided  upon  there  are  many 
points  requiring  attention,  'and  at  this  juncture  discussion  between  buyer  and  maker 
will  prove  of  great  assistance  in  the  design  of  new  buildings  or  alteration  to  existing 
ones.  The  maker  should  furnish  a  plan  showing  the  over  all  dimensions  of  his  machine, 
the  clearances  required  at  the  front,  back,  and  sides,  also  the  total  weight  when 
loaded  with  coal,  and  the  static  load  on  each  wheel.  In  addition,  he  should  state 
the  probable  maximum  load  on  any  wheel  due  to  abnormal  circumstances— such 
as  unevenness  of  the  running  track  or  excessive  thrust  caused  by  stoppage  in  the 
retorts,  etc.  (see  page  45).  If  the  rail  gauge  is  known  the  floor  can  then  be  designed. 
The  majority  of  makers  have  a  regular  form  upon  which  the  necessary  requirements 
for  their  machines  are  set  out,  but  they  can,  of  course,  deviate  from  some  of  them 
(within  reasonable  limits)  without  affecting  the  efficiency  of  the  machine.  In 
obtaining  tenders  the  engineer  should  give  the  salient  requirements  from  the  machine, 
such  as  the  number  of  retorts  to  be  charged,  their  size  and  arrangement,  and  the 
method  of  coal-feeding  proposed. 

So  far  as  working  capacity  is  concerned  separate  charging  and  discharging 
machines  are,  naturally,  capable  of  dealing  with  a  greater  number  of  retorts  than 
are  the  combined  types.  Machines  operating  from  one  side  of  the  bench  only  are 


THE   MECHANICAL   HANDLING   OF   MATERIALS     185 

fast  replacing  those  which  operate  simultaneously  from  both  sides.  In  the  latter 
type  the  number  of  operators  is  doubled,  and  the  capital  cost  is  increased  by 
about  50  per  cent.  Where  a  chain  or  other  working  part  enters  the  retort, 
the  retort  must  be  kept  a  better  shape,  and  usually  requires  scurfing  more  fre- 
quently. 

The  working  portions  of  the  machine  liable  to  breakage  should  be  readily  inter- 
changeable, and  the  engineer  should  know  what  spare  parts  he  is  expected  to  stock, 
as  such  items  have  an  important  bearing  upon  the  efficiency  and  cost  of  upkeep 
of  the  machine.  It  may  be  noted  here  that  the  average  life  of  a  De  Brouwer  belt 
is  from  12,000  to  20,000  tons  of  coal.  The  belt  costs  about  £15  to  replace,  and 
represents  an  expense  of  about  0-225t?.  per  ton  of  coal  handled. 

THE  ARROL-FOULIS  HYDRAULIC  CHARGER 

This  charging  machine  is  usually  operated  in  conjunction  with  a  hydraulic  dis- 
charger. Chargers  are  provided  on  each  side  of  the  retort  bench  and  deliver  the  coal 
from  both  ends  up  to  the  centre  of  the  retort.  Generally  speaking,  a  system  of 
overhead  storage  hoppers  is  provided  in  the  retort  house,  and  by  means  of  suitable 
shoots  the  coal  is  led  into  the  hopper  carried  on  the  front  of  the  charger.  The  hopper 
on  the  machine  is  capable  of  holding  sufficient  coal  to  charge  about  twenty  retorts 
half-way  through.  The  size  of  the  hopper  Varies,  however,  with  the  capacity  of 
the  retort  bench,  and  it  may  hold  anything  from  4  to  8  tons.  Immediately  beneath 
the  hopper  is  fixed  a  revolving  drum  divided  into  compartments  by  radial  partitions. 
By  means  of  a  ratchet  and  pawl  arrangement  a  continuous  rotary  motion  is  imparted 
to  this  drum,  and  the  extent  to  which  it  is  turned  regulates  the  amount  of  coal  falling 
through  from  the  base  of  the  hopper.  On  being  discharged  from  the  drum  the  coal 
falls  into  a  special  trough  which  enters  the  retort  for  a  few  inches.  A  hydraulic 
pusher  ram  with  a  plate  attached  to  the  free  end  then  comes  into  operation  and 
carries  the  coal  charge  into  the  retort.  On  the  backward  stroke  of  the  pusher  bar 
the  coal  drum  is  again  revolved  so  that  another  charge  is  ready  to  be  pushed  forward 
on  the  next  outward  stroke.  By  means  of  a  special  stopper  bar  the  distance  into 
the  retort  travelled  by  the  ram  is  reduced  by  about  18  inches  on  each  stroke,  so  that 
the  coal  is  distributed  comparatively  evenly  along  the  floor  of  the  retort.  For  an 
ordinary  medium  charge  seven  strokes  on  each  side  of  the  bench  are  necessary  to 
complete  the  work,  but  with  the  modern  heavy  charge  the  stopper  bars  should  pre- 
ferably be  removed  so  that  the  retort  may  be  packed.  The  hydraulic  power  is  con- 
veyed to  the  machine  by  flexible  wired  hose  pipe,  and  the  working  pressure  varies 
between  400  and  600  Ib.  per  square  inch.  The  machines  travel  in  front  of  the  benches 
on  a  double-line  track,  and  a  special  three- cylinder  hydraulic  motor  is  provided 
for  this  purpose.  The  total  weight  of  a  machine  with  hoppers  filled  is  about  12 
tons.  Two  chargers  and  one  hydraulic  pusher  are  capable  of  dealing  with  about 
40  retorts  per  hour  with  charges  of  about  18  cwt.  The  capacity  of  the  machines 
is,  therefore,  about  36  tons  of  coal  per  hour.  It  is  difficult  to  give  anything  approach- 
ing exact  figures  for  cost,  but  under  normal  conditions  the  machines,  complete  with 


186 


MODERN   GASWORKS   PRACTICE 


FIG.  147. — THE  ARROL-FOULIS  HYDRAULIC  CHARGER. 

piping  for  connecting  up  to  the  fixed  mains  in  the  retort  house,  could  be  obtained 
for  £600  each. 

THE  HUNTER- BAENETT  PUSHER 

One  of  the  first  hydraulic  pushers  to  be  introduced  was  that  invented  about 
1907  by  Messrs.  Hunter  &  Barnett.  It  is  very  generally  employed  in  conjunction 
with  the  Arrol-Foulis  charging  machinery,  and  is  most  suited  to  this  owing  to  the 
motive  power  being  water.  The  whole  machine  is  self-contained.  The  frame  is 
formed  of  substantial  mild  steel  plates  and  angles  rigidly  connected  together  and 
mounted  on  cast-iron  brackets  (A)  which  carry  the  traversing  carriage  wheels  (B). 
A  three-cylinder  hydraulic  motor  (C)  is  fitted  at  the  front  of  the  machine  and  is 
geared  to  the  carriage  axles  (D)  by  cast-steel  bevel  wheels  (E).  The  method  adopted 


THE   MECHANICAL   HANDLING   OF  MATERIALS     187 

for  pushing  the  coke  through  the  retort  is  as  follows  : — A  powerful  telescopic  ram 
(F)  of  hard,  solid  drawn,  steel  tube,  provided  with  suitable  pusher  head  (G)  and 
fitted  with  internal  drawback  arrangement  is  used.  The  pushing  head  of  the  ram  is 
water-cooled  (H)  to  ensure  that  no  undue  heating  may  occur,  and  the  ram  works 
in  a  cylinder  (K)  of  mild  steel  supported  in  cast-iron  guides  (L).  These  .guides  are 
mounted  on  a  suspended  beam  (M)  carried  by  chains  (0)  at  front  and  back  ends. 


.*» 


FIG.  148. — THE  HUNTER-BARNETT  HYDRAULIC  PUSHER. 


This  suspended  beam  can  be  raised  or  lowered  to  suit  the  several  tiers  of  retorts, 
the  motions  being  obtained  by  means  of  a  hydraulic  ram  (N)  situated  at  the  foot 
of  the  machine.  The  suspending  chains  (0)  are  carried  over  guide  pulleys  (P)  to 
the  points  of  support  at  the  front  and  back  of  the  beam.  The  beam  is  guided  in 
the  machine  frame  so  that  no  side  movement  can  take  place.  All  the  operations 
are  practically  automatic  ;  and  a  suitable  platform  (Q)  is  provided  for  the  attendant, 
with  all  operating  levers  for  valves  and  cocks  placed  in  a  convenient  position  within 


188 


MODERN   GASWORKS   PRACTICE 


his  reach.  The  hydraulic  pressure  may  vary  from  400  Ib.  to  600  Ib.  per  square  inch, 
and  the  water  is  conveyed  by  a  flexible  armoured  hose  pipe  sufficiently  long  to 
carry  the  machine  over  a  number  of  beds  of  retorts.  When  the  outreach  of  the 
pipe  is  attained,  the  hose  connexion,  as  with  the  Arrol-Foulis  chargers,  is  shifted 
to  the  next  swivel  joint  on  the  main  supply  pipe  and  the  machine  carried  on.  Swivel 
joints  are  placed  on  the  pressure  main  and  are  spaced  to  suit  the  length  of  the  flexible 
hose  pipe  and  adjusted  to  suit  the  particular  arrangement  used  in  the  retort  house. 
The  cost  of  the  machine,  complete  with  piping  for  connecting  up  to  fixed  hydraulic 
mains  in  the  retort  house,  is  about  £500. 

' 

THE   WlLLIAMS-MACPHEE   PUSHEK 

The  Williams-MacPhee  hydraulic  pusher  is  one  of  the  most  recent  of  these 
machines  introduced  and  comprises  many  commendable  features.  The  simplicity 
of  the  entire  arrangement  is  its  chief  recommendation.  The  machine  consists  of 
a  pusher  constituted  of  an  outer  cylinder  containing  two  telescopic  rams  of  sufficient 


FIG.  149. — WORKING  DBA  WING  OF  THE  WILLIAMS-MACPHEE  PUSHER. 


THE   MECHANICAL   HANDLING   OF   MATERIALS     189 

length  to  extend  through  a  20-foot  retort.  Each  ram  is  provided  with  a  stopper 
at  its  rear  end,  and  on  the  smaller  solid  ram  a  pusher  plate,  similar  in  shape  to  the 
retort  but  slightly  smaller,  is  fitted.  The  ram  is  extended  by  admitting  hydraulic 
pressure  at  the  back  of  the  cylinder,  and  by  means  of  a  special  automatic  return 
valve  the  pusher  is  withdrawn  when  the  full  extent  of  its  stroke  has  been  reached. 


FIG.  150. — THE  WILLIAMS-MACPHEE  PUSHER. 

Withdrawal  is  effected  by  a  chain,  attached  to  the  pusher  head,  which  passes  around 
a  pulley  connected  to  a  subsidiary  hydraulic  ram.  This  withdrawing  ram  is  pulled 
into  its  cylinder  by  the  tension  of  the  chain  during  the  outward  stroke.  The  auto- 
matic return  is  arranged  for  by  introducing  a  tappet  rod  connected  by  a  lever  to 
the  distributing  valve  of  a  small  actuating  ram,  the  stroke  of  which  reverses  the 
controlling  valve  and  opens  the  exhaust  port  to  the  pusher  cylinder,  thus  withdrawing 
the  telescopic  rams.  This  tappet  is  engaged  by  the  ram- head  at  a  pre- determined 


190 


MODERN  GASWORKS   PRACTICE 


Telescopic  Shoot 
Tundislt 


Grooved  Pulley 
1  metre  diam. 


point  on  the  outer  stroke.  In  practice  it  is  found  that  the  outward  discharging 
stroke  takes  about  10  seconds  to  be  completed,  whilst  the  return  stroke  is  accom- 
plished in  8  seconds.  The  chief  merit  of  this  type  of  pusher  lies  in  the  fact  that  there 
are  only  four  glands  to  pack,  whilst  only  one  of  them  has  to  withstand  the  severe 
effects  of  entering  the  retort.  The  wear  and  tear  is,  in  fact,  almost  inconsiderable, 
a  pusher  chain  lasting  for  about  twelve  months  before  it  has  finally  to  be  discarded. 
The  cost  of  the  machine,  complete,  is  about  £420. 

THE  DE  BROUWER  STOKING  MACHINE 

The  first  charging  machine  involving  the  projector  principle  was  introduced 
~by  M.  De  Brouwer,  gas  engineer  at  Bruges.  The  outstanding  advantage  of  this 
machine  compared  with  others  in  use  at  the  time  was  its  ability  to  charge  a  full- 
sized  retort  from  one  side  only,  thus  avoiding  the  necessity  of  installing  machines 
on  both  sides  of  the  bench.  The  whole  apparatus  is  extremely  simple,  and  consists 

of  a  steel  frame  carrying 
a  large  grooved  pulley, 
three  band  pulleys  for 
guiding  a  broad  band,  a 
driving  motor,  and  a  tele- 
scopic feeding  shoot  for 
coal.  The  principle  of 
operation  will  be  readily 
understood  by  reference 
to  the  line  diagram  (Fig. 
151).  The  three  band 
pulleys  are  arranged  on 
the  inside  of  the  broad 
endless  coal  belt,  and 
are  so  placed  that  this  belt  is  made  to  take  about  a  quarter  turn  round  the  large 
grooved  pulley.  The  coal  band  bears  on  the  two  flat  flanges  of  the  pulley  and 
•causes  the  pulley  to  revolve  at  the  same  speed  as  the  belt.  The  band  is  driven  by 
ordinary  belt  drive  on  to  the  front  band  pulley  from  an  ordinary  shunt  wound 
variable  speed  electric  motor  of  4  to  6  b.h.p.,  having  a  speed  variation  of  from 
750  to  1,500  revolutions  per  minute.  Equally  good  results,  however,  may  be  ob- 
tained with  compressed  air  motors  or  rope  drives.  The  ordinary  type  of  machine 
as  now  in  general  use  is  illustrated  in  Fig.  152.  From  this  it  will  be  seen  that 
at  the  upper  portion  of  the  travelling  framework  there  is  a  small  hopper  or  measuring 
•chamber  into  which  the  coal  is  fed  from  continuous  hoppers  erected  in  the  retort 
house.  A  telescopic  shoot  leads  from  the  measuring  chamber  to  the  groove  of  the 
large  pulley,  thus  the  delivery  tundish  for  coal  automatically  adjusts  itself  as  the 
machine  is  raised  or  lowered  to  the  various  tiers 'of  retorts. 

The  operation  of  charging  is  as  follows  : — Assuming  that  the  overhead  hopper 
is  already  full,  the  operator  first  starts  the  motor  and  moves  the  handle  of  his  speed- 
xegulating  rheostat  into  'the  position  necessary  for  giving  the  projector  belt  the 


Electric  Motor  Power 
to  start  Machine 
10-15  amps  at 
220  volts. 


FIG.  151. — LINE  DIAGRAM  SHOWING  PRINCIPLE  OF  DE  BROUWER 
PROJECTOR. 


THE   MECHANICAL   HANDLING   OF   MATERIALS     191 


desired  speed.  This  speed  varies  according  to  the  length  of  the  retort,  the  class  of 
coal  used,  and  the  thickness  of  the  charge  required,  and  must  first  be  found  by  trial. 
With  ordinary  broken  coal  and  charges  of  about  9  cwt.,  the  belt  speed  should  be 


FIG.  152. — THE  DE  BROUWER  PROJECTOR. 

about  2,300  feet  per  minute,  but  for  perfectly  full  charges  a  greater  speed  will  be 
necessary.  When  the  required  speed  has  been  attained,  the  hopper  door  is  opened 
and  the  coal  falls  into  the  space  between  the  belt  and  pulley.  The  centrifugal  force 
exerted  on  the  coal  as  the  belt  passes  round  the  circumference  of  the  grooved  drum 
keeps  the  coal  in  contact  with  the  belt,  so  that  the  velocity  of  the  coal  becomes 
the  same  as  the  velocity  of  the  belt.  As  the  coal  reaches  the  front  pulley  the  belt 
is  suddenly  deflected  round  the  pulley,  and  the  momentum  keeps  the  coal  travelling 
forward  into  the  retort  in  a  continuous  stream.  The  distance  through  which  the 
coal  travels  is  gradually  de- 
creased as  the  operation  of 
•charging  proceeds,  this  being 
effected  by  a  gradual  reduc- 
tion in  speed  of  the  band. 
The  whole  operation  of 
charging  takes  from  20  to  30 
seconds,  according  to  the 
amount  of  coal  put  into  the 

retort. 

ml  ,.  .  FIG.  153. — SLANTING  STOP  FOR  USE  WITH  PROJECTORS. 

ihe     earlier    machines 

were  suspended  from  an  overhead  carriage  and  traversed  along  by  hand,  but  as 
this  was  a  somewhat  slow  process  the  later  machines  were  arranged  in  a  travelling 
carriage  or  frame,  and  were  driven  by  power. 


192  MODERN   GASWORKS   PRACTICE 

With  projecting  chargers  of  this  type  some  form  of  obstruction  or  stop  is  required 
at  the  further  end  of  the  retort  to  prevent  the  coal  piling  up  on  the  cool  mouth- 
piece. An  ordinary  piece  of  plate  with  a  supporting  rod  at  the  back  is  generally 
used  for  the  purpose.  It  is  as  well  to  remember,  however,  that  the  vertical  stop 
originally  employed  frequently  accounted  for  a  small  portion  of  coal  remaining  un- 
carbonized  at  the  end  of  the  distillation  period,  and  it  is  preferable  to  make  use 
of  the  slanting  stop  as  seen  in  Fig.  153. 

The  following  are  the  more  interesting  points  connected  with  the  De  Brouwer 
machine : — 

Large  pulley  :  Diameter,  1  metre  (39-3  inches). 
Width  on  face,  15  inches. 
Width  of  groove,  8  inches. 

Depth  of  groove,  3f  inches.  . 

Average  speed  of  pulley,  220  revolutions  per  minute. 
Average  speed  of  coal  band,  2,300  feet  per  minute. 
Power  required,  10  to  15  amperes  at  220  volts. 

The  cost  of  the  machine,  complete  with  wiring,  is  about  £8CO,  depending  upon 
the  number  of  tiers  of  retorts  and  the  method  of  coal  feeding. 

THE  JENKINS-DE  BROUWEE  PUSHER 

This  machine  has  a  strongly  braced  framework  of  steel  channels  and  angles, 
forming  a  travelling  carriage,  and  is  fitted  with  wheels  for  running  along  rails  in  front 
of  the  retort  bench,  preceding  the  De  Brouwer  charger.  An  electric  motor  and 
gearing  box  is  fixed  on  the  main  channels  of  the  frame,  on  the  left-hand  side,  for  hoist- 
ing the  pusher  ram  to  suit  the  various  tiers  of  retorts  and  also  for  propelling  the 
machine  along  the  rails.  The  motor  is  of  7|  b.h.p.,  entirely  enclosed,  provided 
with  end  covers,  dirt  and  dust  proof,  and  connected  by  a  suitable  coupling  to  the 
first  motion  shaft  in  the  gearing  box.  The  gearing  box  is  fitted  with  a  worm  and 
worm  wheel  and  spur  gearing,  also  a  clutch  for  connecting  either  the  hoisting  or 
propelling  gear  to  the  motor.  One  spur  pinion  in  the  gearing  box  gears  with  a 
spur  wheel  on  one  of  the  axles  of  the  machine,  and  the  worm  wheel  shaft  carries  a 
chain  drum  round  which  the  hoisting  chains  work.  These  chains  pass  upwards 
from  the  drum,  over  pulleys  on  the  machine  frame,  down  again  and  round  pulleys 
on  the  hanging  frame  carrying  the  telescopic  ram,  and  back  to  a  point  near  the 
top  of  the  frame,  where  they  are  anchored. 

The  telescopic  ram  is  in  three  parts,  the  first  or  inner  length  being  formed  of 
a  strong  mild-steel  bar  cut  out  of  the  solid  and  having  drilled  holes  for  the  driving 
sprocket  teeth  and  a  plate  end.  The  plate  end  carries  a  hood  or  scoop  at  the  top 
to  hold  the  coke  and  keep  it  from  crushing  up.  This  inner  bar  slides  within  the 
second  length.  Inside  the  front  end  of  the  second  length  is  fixed  a  suitable  stop  which 
fits  into  a  groove  on  the  top  side  of  the  first  length,  so  as  to  fix  the  length  of  stroke 
of  the  first  bar  and  to  ensure  it  having  a  rigid  bearing  within  the  second  length  when 
fully  extended.  The  section  of  the  second  length  is  made  up  of  two  steel  channels 
connected  together  by  means  of  steel  cover  plates.  This  length  has  fitted  at  the 


THE   MECHANICAL   HANDLING   OF   MATERIALS     193 

back  end  four  rollers  running  on  cast-steel  pivots.  The  rollers  are  of  suitable  size 
for  running  within  the  channels  which  form  the  third  length.  The  stroke  of  the 
second  length  is  governed  by  stops  fixed  in  the  front  end  of  the  third  length  with 
which  the  front  rollers  come  in  contact,  thus  ensuring  a  rigid  bearing  when  fully 
extended.  The  third  length  is  of  similar  but  larger  section  to  that  of  the  second 
length.  This  length  is  also  fitted  with  four  rollers  running  on  cast-steel  pivots. 
These  rollers  are  of  suitable  size  for  running  within  the  fixed  channels  which  form 
the  lower  portion  of  the  hanging  frame,  which  is  fitted  with  stops  at  the  front  end 
so  that  the  third  length  also  has  a  rigid  bearing  when  at  its  extreme  outward 
stroke. 

On  the  underside,  at  the  front  end  of  the  hanging  frame,  there  is  a  steel  rack 


FIG.  154. — THE  JENKINS  DE  BROUWER  DISCHARGING  PUSHER,  SHOWING  THE  TELESCOPIC  RAM  FULLY 

EXTENDED. 

pinion  keyed  to  a  shaft  on  the  end  of  which  is  fitted  a  steel  spur  wheel  to  gear  with 
a  similar  wheel  on  a  shaft  fixed  above.  To  this  latter  shaft  is  keyed  a  strong  sprocket 
chain  wheel.  The  pinion  gears  in  the  rack  forming  the  first  bar  and  also  gears 
with  the  second  and  third  portion,  consisting  of  cast-steel  jointed  links,  which  pass 
upwards  round  the  guide  path  at  the  back  end  of  the  frame  when  the  pusher  bar 
is  out  of  the  retorts.  A  water  spray  is  fixed  at  the  front  end  of  the  hanging  frame 
for  cooling  the  telescopic  ram. 

Motion  is  transmitted  from  the  pusher  motor  by  means  of  a  pinion  driving 
a  spur  wheel  keyed  at  one  end  of  an  intermediate  shaft  having  at  the  other  end  a 
sprocket  chain  pinion  for  driving  (by  means  of  one  of  Hans  Renold's  patent  roller 
chains)  the  chain  wheel  near  the  end  of  the  hanging  frame. 

The  telescopic  ram  is  driven  by  an  electric  motor  which  is  an  exact  duplicate 
of  the  hoisting  and  propelling  motor,  and  which  is  carried  on  a  cast-iron  bedplate 

o 


194 


MODERN   GASWORKS   PRACTICE 


bolted  to  the  channels  of  the  hanging  frame.  The  current  for  the  two  motors  is 
collected  from  two  overhead  bare  copper  conductors  by  means  of  two  trolley  poles 
fixed  near  the  top  of  the  machine  frame.  From  these  poles  the  current  is  led  by 
means  of  stranded  copper  insulated  conductors  carried  in  steel  conduits  to  the 
switch  and  connexion  box  on  the  platform.  The  connexion  box  is  fitted  with  the 


FIG.  155. — DRAKE'S  COMBINED  PROJECTOR  AND  PUSHER. 

necessary  double  pole  switch,  automatic  circuit  breaker  and  distributing  fittings 
From  this  box  the  current  is  led  to  the  reversing  controller  of  the  hoisting  and  pro- 
pelling motor  and  to  two  bare  conductors  strained  vertically  on  one  side  of  the 
machine  frame.  The  motor  driving  the  telescopic  ram  collects  its  current  from 
these  conductors  by  means  of  two  short  trolley  poles  fixed  to  the  hanging 


I 

THE   MECHANICAL   HANDLING   OF   MATERIALS     195 

frame.  An  automatic  cut-off  is  arranged  so  that  the  controller  is  returned  to 
the  "off"  position  at  each  end  of  .the  stroke  of  the  ram,  also  when  the  hanging 
frame  is  moved  to  the  top  and  bottom  positions.  A  foot  brake  is  attached  to 
the  machine  for  bringing  it  to  rest  exactly  in  front  of  the  retort  which  is  to  be 
discharged. 

The  cost  of  the  pusher  is  about  £800,  complete  with  wiring,  but  if  combined 
with  the  projector  on  the  same  wheel-base  the  two  machines  may  be  obtained  for 
about  £1,150,  depending  upon  the  number  of  tiers  in  which  the  retorts  are  set. 

DRAKE'S  PROJECTOR  AND  PUSHER 

Drake's  stoking  machine,  in  which  the  projector  and  pusher  are  mounted  on 
a  common  wheel-base,  is  illustrated  in  Fig.  155.  The  principle  of  the  projector 
differs  entirely  from  that  of  De  Brouwer.  The  outer  casing  (4)  contains  a  rotor  very 
similar  in  construction  to  the  paddle-wheel  of  a  steamer,  with  the  exception  that 


FIG.  156. — DRAKE'S  PUSHER,  SHOWING  CONSTRUCTION  OF  THE  CHAIN. 


196  . 


MODERN   GASWORKS   PRACTICE 


it  is  divided  down  the  centre  so  that  with  a  feed  at  either  side  the  coal  is  charged 
into  the  retort  in' two  streams.  These  streams  converge  in  the  retort  and  form  the 
charge.  Owing  to  the  manner  in  which  the  coal  feed  is  arranged  the  lumps  of  coal 
are  not  knocked  into  the  retort  by  the  blades  of  the  rotor,  but  they  are  picked  up 
and  thrown  in  by  centrifugal  force.  It  will  be  seen  that  the  coal  drops  from  a  storage 
(1)  hopper  direct  into  a  telescopic  shoot  (2)  which  in  turn  delivers  to  a  breeches 
shoot  (3)  feeding  into  both  sides  of  the  projector  simultaneously.  An  apron  (5)  is 
fitted  to  the  front  of  the  casing  in  order  to  prevent  any  spilling  of  coal. 

The  construction  of  the  discharging  pusher  will  be  readily  followed  from 
Fig.  156.  The  ram  is  of  taper  construction,  and  the  narrow  end  lets  down  into  the 
wider  end  when  folding  round  the  drum.  The  chain  is  constructed  from  mild 
steel,  and  the  links  are  fitted  with  renewable  hard  steel  sliding  pieces  and  hard 
steel  horns.  To  one  side  of  the  shaft  of  the  main  drum  is  keyed  a  phosphor-bronze 
machine-cut  worm  wheel  driven  by  a  mild-steel  worm  running  in  an  enclosed 
oil-bath. 

DISCHARGING  CHARGERS 

One  of  the  most  interesting  modern  developments  connected  with  the  operation 
of  gas  retorts  is  the  discharging  charger,  which  effects  the  expulsion  of  the  coke  and 
the  refilling  with  coal  in  a  single  stroke.  The  first  machine  of  this  kind  to  be  intro- 


Fio.  157. — THE  FIDDES-ALDRIDGE  "  CHAIN." 


duced  was  the  Fiddes-Aldridge,  which  accomplishes  the  work  by  means  of  a  specially 
designed  push-plate  conveyor  consisting  of  two  vertical  parallel  plates  but  with  no 
bottom.  These  plates  are  hinged  about  every  3  or  4  feet,  and  are  maintained  in 
position  by  cross-bars  arched  to  the  same  radius  as  the  crown  of  the  retort.  Plates 


THE   MECHANICAL   HANDLING   OF  MATERIALS    197 

are  suspended  from  the  cross-bars,  and  are  so  arranged  that  when  the  conveyor  or 
"  chain  "  enters  the  retorts  the  plates  remain  vertical,  but  are  free  to  lift  when  the 
chain  is  withdrawn.  Each  of  the  swinging  plates  pushes  a  certain  amount  of  coal 
into  and  along  the  floor  of  the  retort ;  whilst  on  the  backward  stroke  the  plates  lift 
automatically  and  assist  in  levelling  the  charge.  The  construction  and  working  of 
the  chain  will  be  clearly  followed  from  Fig.  157. 


FIG.  158. — THE  FIDDES-ALD  RIDGE  DISCHARGING  CHARGER. 


A  measuring  chamber  over  the  chain  receives  the  coal  from  continuous  hop- 
pers, the  coal  being  dropped  through  a  shoot  into  the  chain  as  the  latter  passes  for- 
ward into  the  retort.  The  chain  passes  round  a  vertical  polygon  wheel,  which  is 
usually  driven  by  electricity,  mounted  on  a  steel  framework.  Two  frameworks  are 
provided  (an  inner  one  and  an  outer),  the  inner  frame  rising  or  falling  inside  the 
larger  one  so  that  any  tier  of  retorts  may  be  charged.  A  hinged  apron  plate  is 


198 


MODERN   GASWORKS   PRACTICE 


lowered  into  the  front  of  the  retort  mouthpiece,  and  acts  as  a  connecting  trough 
between  the  retort  and  the  machine,  the  bottom  of  the  apron  plate  forming 
the  bottom  of  the  chain.  The  front  length  of  the  chain  (called  the  "  fire- length  ") 
is  very  strongly  constructed,  and  acts  as  a  pusher  head  during  the  outward 
stroke.  The  operations  of  charging  and  discharging  are  performed  simultane- 
ously, about  30  seconds  being  necessary  to  empty  and  refill  a  20-foot  retort. 
The  external  dimensions  of  the  machine  are  about  8  feet  6  inches  long  by 
13  feet  high.  The  standard  pattern  of  the  Fiddes-Aldridge  machine  is  fully  illus- 
trated in  Fig.  158,  from  which  part  of  the  framework  has  been  removed  so  as  to  give 
a  clearer  view  of  the  driving  wheel  and  chain. 


FIG.  159. — THE  NEW  TYPE  OF  FIDDES-ALDRIDGE  MACHINE,  FOR  DELIVERING  FULL  CHARGES. 

(SECTION  OF  THE  CHAIN.) 

The  machine  was  originally  introduced  at  a  time  when  many  engineers  still 
favoured  the  light  charge  of  coal,  and  one  of  the  few  disadvantages  it  embraces  is 
its  inability  to  completely  fill  the  ordinary  retort  with  coal.  This  is  due  to  the  fact 
that  a  certain  amount  of  room  must  be  left  in  the  crown  of  the  retort  for  the  return 
of  the  chain  plates.  In  the  latest  type  of  machine,  however,  this  drawback  has 
been  overcome,  and  retorts  may  now  be  completely  filled  if  so  desired.  The  main 
polygonal  driving-wheel  is  still  retained,  and  the  modification  has  chiefly  occurred 
in  the  construction  of  the  chain.  All  push-plates  are  dispensed  with,  and  instead 
there  is  a  chain  carrier  inside  which1  runs  a  flexible,  conveyor.  The  chain  carrier 
and  conveyor  are  set  in  motion  and  enter  the  retort  together,  the  conveyor  depositing 
coal  along  the  bottom  of  the  retort  until  the  far  end  is  reached.  The  speed  of  the 


199 


200 


MODERN   GASWORKS   PRACTICE 


flexible  conveyor  is  then  increased  as  both  are  withdrawn,  and  coal  is  thrown  over 
the  end  of  the  conveyor  at  such  a  rate  as  to  fill  the  retort  completely.  By  varying 
the  relative  speeds  of  the  chain  carrier  and  the  running  chain  or  conveyor  any  sized 
charge  can  be  placed  in  the  retort.  The  flexible  conveyor  runs  the  full  length  of 
the  carrier  chain,  so  that  there  is  in  reality  one  conveyor  inside  another.  As 
explained  above,  a  thin  layer  of  coal  is  laid  on  the  bottom  of  the  retort  during  the 
outward  discharging  stroke,  but  this  is  not  essential,  and,  if  so  desired,  the  whole 
of  the  charge  may  be  delivered  over  the  end  of  the  conveyor  during  the  return  stroke. 
The  construction  of  the  machine  will  be  followed  by  reference  to  Fig.  159,  in  which 
the  flexible  and  carrier  conveyors  are  clearly  seen. 

THE  GUEST- GIBBONS  DISCHARGING  CHARGER 

This  machine  is  one  of  those  most  recently  introduced,  and  is  capable  of  simul- 
taneously discharging  and  charging  a  retort  so  that  the  fresh  coal  lies  within  about 
5  inches  of  the  crown  of  the  retort.  (The  machine  has  recently  been  adapted 
to  give  a  completely  full  charge.)  The  general  construction  of  the  apparatus  is 
shown  in  Fig.  160.  The  portion  of  chief  interest  is  the  chain,  which  combines  the 
coke  pusher  and  means  for  introducing  the  charge.  The  coke  is  discharged  by  the 
pusher  head  on  the  outward  stroke,  when  the  position  -of  the  chain  is  as  seen  in  Fig. 


FIG.  161. 


FIG.  162. 


FIG.  163. 
THE  GUEST-GIBBONS  CHAIN. 

161.  The  coal  is  then  charged  in  by  two  or  three  strokes  of  the  chain,  according  to 
the  length  of  the  retort.  The  coal,  falling  into  the  chain  from  overhead  chambers, 
is  carried,  into  the  retort  by  the  drag  bars  and  push-plate  (Fig.  162).  The  chain  is 
composed  principally  of  two  separate  members,  one  inside  the  other,  and  when  at 
rest  on  the  machine  is  supported  by  a  trough.  The  outer  member  carries  the  push- 
plate  for  discharging  the  coke,  and  the  inner  member  supports  at  its  front  end  an 
open  grid  or  drag-bar  upon  which  the  coal  is  fed.  A  shutter  at  the  bottom  of  the 


THE   MECHANICAL  HANDLING   OF   MATERIALS    201 

feed  shoot  in  the  measuring  chamber  automatically  cuts  off  the  supply  of  coal  to 
the  drag-bars  when  a  sufficient  quantity  has  been  taken  for  one  stroke.  The  position 
of  the  chain  during  the  backward  stroke  is  indicated  in  Fig.  163.  The  tray  plate 
connecting  the  machine  with  the  retort  is  of  similar  size  and  section  as  the  retort ; 


FIG.  164. — THE  GUEST-GIBBONS  MACHINE. 

hence  smoke  and  dust  are  to  a  great  extent  eliminated.  Three  electric  motors  are 
provided,  one  for  each,  operation  of  hoisting,  travelling,  and  charging.  The  time 
occupied  for  the  complete  operation  of  discharging  and  refilling  is  about  2  minutes. 
The  cost  of  the  machine,  complete  with  wiring,  is  from  £1,000  to  £1,200,  depending 
on  the  type  and  on  the  number  of  tiers  in  which  the  retorts  are  set. 

SUBSIDIARY  RETORT-HOUSE  MACHINES 

During  recent  years  machines  have  been  introduced  into  the  retort  house  for 
performing  subsidiary  duties  such  as  the  augering  of  ascension  pipes,  the  clinkering 
of  producers,  and  the  poking  down  of  fuel  into  the  latter.  Owing  to  the  comparative 
immunity  from  stopped  pipes  in  the  modern  retort  house,  however,  the  augering 
machine  has  practically"  disappeared,  but  apparatus  for  performing  the  other 
duties  mentioned  seems  likely  to  become  a  more  or  less  essential  auxiliary  in  the 
case  of  larger  installations.  With  the  introduction  of  the  many  forms  of  labour- 
saving  machinery  the  gasworker  is  approaching  a  golden  age  as  far  as  working  con- 
ditions are  concerned,  and  these  latest  machines  may  certainly  be  said  to  eliminate 


202 


MODERN   GASWORKS   PRACTICE 


the  last  remaining  portion  of  gasworks  labour  in  which  considerable  effort  is  entailed 
in  the  face  of  severe  heat. 

CLINKERING  MACHINES 

The  mechanical  clinkering  machine  shown  in  Figs.  165  and  166  may  be  operated 
by  hydraulic,  pneumatic,  or  steam  power,  and  effectively  removes  the  heavy  layer 

of  clinker  formed  at  the  base 
of  the  fuel-bed  in  about  one- 
fifth  the  time  required  with 
manual  work.  There  is  no 
particularly  novel  feature 
about  its  construction,  which 
is  on  the  principle  of  a  ram, 


the  head    being: 


designed 


to 


FIG.  165.— MECHANICAL  CLINKERING. 


cut  through  hard  masses  of 
slag.  The  nature  of  the 
clinker  collecting  in  a  retort- 
bench  producer  varies  to  a 
considerable  extent  with  the 
quality  of  the  coal  carbonized 

and  the  proportion  of  ash  in  the  coke,  and  it  is  when  inferior  coals  are  in  use  that 
the  machine  is  seen  at  its  best.  As  an  instance  of  the  saving  effected  it  may  be 
mentioned  that  at  one  of  the  larger  London  gasworks  a  single  fireman  was  capable 
of  dealing  with  three  producers  during  his  eight-hour  shift ;  that  is  to  say,  he  was 
deputed  to  clinker  retort  settings  yielding  about  half  a  million  cubic  feet  of  gas 


FIG.  106. — GILL'S  MECHANICAL  CLINKERING  MACHINE. 


THE   MECHANICAL   HANDLING   OF   MATERIALS     203 

per  diem.  With  the  aid  of  the  machine  the  man  increased  his  daily  number  of  fires 
to  eight,  and  his  gas  output  to  1J  million  cubic  feet.  There  are  other  attendant 
advantages,  such  as  a  saving  of  fuel,  owing  to  the  shortened  period  for  which  the 
doors  are  open,  and  decreased  wear  and  tear  on  the  false  firebars. 

THE  FURNACE  POKER 

The  object  of  this  machine  is  to  relieve  the  retort-house  hands  of  a  portion  of 
their  duties  which  demands  much  physical  exertion.  In  the  ordinary  way  the  heated 
coke  as  it  falls  from  the  retort  is  poked  down  into  the  producer  and  levelled  off  by 
manual  labour.  For  this  reason  it  is  customary  to  employ  more  men  on  the  stage 
during  the  "  firing  draw  "  than  is  the  case  when  the  coke  is  merely  pushed  out  and 
taken  to  the  stock  heap.  By  installing  the  poker  the  necessity  for  extra  labour  is 
averted,  and  the  work  can  be  more  quickly  and  effectively  carried  out.  The  hydrau- 
lic type  of  machine  is  shown  in  Fig.  167.  As  will  be  seen,  it  is  customary  to  attach 


FIG.  167. — GILL'S  FURNACE  POKER. 

the  poker  to  the  side  of  the  framework  of  one  of  the  "  pushers,"  so  that  no  separate 
travelling  carriage  is  necessary.  The  poker  itself  consists  of  a  rod  9  feet  long  by  3 
inches  wide  by  f  inch  in  thickness,  and  is  provided  with  a  cast-iron  fish-tailed  head. 
It  is  actuated  by  two  rams  each  about  4  feet  in  length  and  1|  inches  in  diameter, 
attached  by  means  of  chains  to  a  slipper  fixed  at  the  back  end  of  the  rod.  One  ram 
is  used  for  the  forward  stroke  and  one  for  the  backward  stroke,  the  length  of  the 
stroke  being  6  feet.  The  time  taken  to  charge  a  producer  with  about  9  cwts.  of  coke 
is  approximately  25  seconds. 

COMPARATIVE   COSTS   OF   RETORT-HOUSE   LABOUR 

It  is  only  possible  to  draw  a  general  comparison  between  the  costs  of  operating 
retort  houses  under  various  conditions.     Very  much  naturally  depends  upon  the 


204  MODERN   GASWORKS   PRACTICE 

magnitude  of  the  installation,  the  proportion  of  the  work  which  is  carried  out  by 
mechanical  means,  and  whether  or  not  the  men  are  worked  up  to  their  full 
•capacity.  A  retort  house  may  be  fitted  with  the  most  economical  type  of  charging 
and  discharging  machinery,  and  yet  be  served  in  a  more  or  less  primitive  manner 
as  regards  the  intake  of  coal  and  the  disposal  of  coke.  The  methods  of  conducting 
the  retort-house  work  may  be  classified  under  three  headings  : — 

(1)  Manual  labour  entirely,  for  all  works  up  to  about  20  million  cubic  feet  per 
annum. 

(2)  Manual  machines,  for  works  between  20  and  120  million  cubic  feet  per 
annum. 

(3)  Power  machines,  for  works  making  more  than  120  million  cubic  feet  per 
annum.     It  should  be  noted  that  there  are  a  limited  number  of  works  making  less 
than  this  quantity  in  which  power  machinery  is  installed,  but  in  general  this  limit 
may  be  adhered  to  unless  exceptional  considerations  come  into  account. 

For  the  purpose  of  comparison  it  is  preferable  to  base  the  cost  of  labour  in  the 
retort  house  on  the  tons  of  coal  handled,  and  in  the  following  table  the  figures  given 
include  all  items,  i.e.  the  charges  for  taking  in  and  breaking  coal,  wear  and  tear, 
charging  and  discharging,  the  disposal  of  coke  and  ashes,  etc.  : — 

COMPARATIVE  COSTS  FOR  OPERATING  RETORT  BENCHES 
Hand  charging  and  discharging.     2s.    6d.  to  3s.  per  ton  of  coal   handled   (depending  upon 

size  of  installation). 

"Manual"  machines.         .          .     Is.  Wd.  to  2s.  2d.  „    .  „  „ 

Power  machines  (older  types)     .     Is.  3d.  „  „  „ 

Projector  and  pusher          .          .     Is.  to  Is.  2d.  „  „  „ 

Discharging  chargers  .         .          .     lOd.  to  Is.  „  „  „ 

Inclined  retorts  .          .          .Is.  2d.  „  „  „ 

Vertical  retorts  (both  types)       .     4d.  to  6d.  „  „  „ 

Chamber  ovens  (Munich  type)    .     l%d.  to  3d.  „  „  „ 

ELEVATING   AND   CONVEYING  MACHINERY 

Only  in  exceptional  cases  is  the  gasworks  engineer  in  a  position  to  design  in 
'detail  mechanical  plant  for  the  handling  of  his  materials,  and  as  there  are  to-day 
many  contractors  who  are  specialists  in  this  type  of  work  there  should  be  no  hesita- 
tion in  placing  the  matter  in  their  hands.  If  this  is  done,  standardized  details  will 
not  be  departed  from,  and  the  system  will  gain  in  efficiency  and  economy.  In 
obtaining  tenders  or  settling  upon  new  plant  there  are  several  points  which  the 
engineer  with  the  erection  of  machinery  in  view  should  bear  in  mind.  He  should 
supply  to  the  contractor  figures  showing  the  capacity  of  plant  in  tons  per  hour, 
stating  the  conditions  of  working.  In  return,  the  contractor  should  be  asked  for 
the  following  particulars  : — 

(a)  Breadth  of  elevator  buckets  or  conveyor  band. 

(6)  Pitch  of  buckets,  and  speed  of  chain  or  band.  The  engineer  should 
provisionally  fix  the  speed,  laying  down  a  certain  limit. 

(c)  Detailed  specification  of  buckets  and  chain ;    or, 

(d)  Detailed  specification  of  belt. 


THE   MECHANICAL   HANDLING   OF   MATERIALS    205 


(e)  Particulars  of  arrangement  for  taking  up  elongation  of  the  chain  or  belt, 
and  the  facilities  afforded  for  the  renewal  of  working  parts. 

(/)  Details  of  framing  and  supporting  girders,  with  the  thickness  of  all  sheets 
and  plates  in  hoppers,  etc. 

1(g)  Power  required  for  driving  ;  also  types  and  sizes  of  motors  or  engines  supplied,, 
and  surplus  power  provided. 

(h)  Arrangements  for  lubrication  ;  also  what  provision  is  made  for  the  lessening 
of  friction. 

(i)  If  electrically  driven,  details  of  cabling,  starters,  and  accessories  (if  any) 
supplied. 

No  general  rule  can  be  laid  down  as  to  the  limiting  size  of  a  works  on  which  coal 
or  coke-handling  plant  can  be  profitably  employed.  It  may  be  taken,  however, 
that  a  minimum  size  plant  (including  buildings)  would  cost  from  £1,500  to  £2,000 ; 
and  16  per  cent,  on  this  outlay  represents  about  £300.  Accordingly  a  60  million 
per  annum  works  would  have  to  save  Is.  2d.  per  ton  of  coal  used  before  the 
machinery  could  be  shown  to  be  profitable. 

There  is  a  certain  similarity  between  elevators  and  conveyors  in  that,  so  far 
as  types  employed  on  gasworks  are  concerned,  they  consist  almost  solely  of  endless- 
belts  or  chains  passing  around  two  terminal  pulleys.  To  such  chains  are  attached 
suitably  shaped  buckets  or 

draw-bars.     The  length  of  the  Adjustable  Bearings 

conveyor  or  elevatoris 
measured  from  centre  to  centre 
of  the  terminal  sprockets.  It 
is  the  common  practice  to  con- 
struct chains  for  these  pur- 
poses from  malleable- iron  or 
steel  links ;  and,  as  after  a 
certain  period  of  working  the 
metal  takes  up  a  permanent 
stretch,  it  is  usually  necessary 
to  provide  some  form  of  auto- 
matic tightening  gear.  With 
the  simple  elevator  it  will 
generally  be  found  sufficient  if 
the  bottom  sprocket  is  fitted 

with  adjustible  bearings,  so  that  any  extension  maybe  periodically  taken  up.  For 
elevators  of  larger  capacity  a  single  chain  is  insufficient,  and  multiple  strands  have 
to  be  resorted  to.  An  objection  to  these  is  that  the  different  strands  (usually  two) 
will  stretch  unevenly,  thus  throwing  the  buckets  out  of  alignment  with  one  another. 
This  particularly  applies  to  the  malleable-iron  type  ;  and  in  long  lengths  of  conveying 
machinery  it  is  usual  to  provide  some  form  of  adjustment  to  alleviate  the  defect, 

1  The  engineer  will  generally  prefer  to  purchase  his  own  motors,  arranging  for  the 
surplus  of  power  he  thinks  advisable. 


i     C 

1    \ 

Conveyor  Chain 

itt-i- 

| 

« 

FIG.  168.— CHAIN-TIGHTENING  DEVICE. 


206  MODERN   GASWORKS   PRACTICE 

distinct  from  that  employed  for  automatically  taking  up  any  slack.  The  device 
'for  tightening  each  chain  which  is  employed  in  many  conveyors  is  shown 
in  Fig.  168,  whilst  Fig.  169  illustrates  the  means  introduced  for  taking  up 
the  total  increase  of  length  of  the  chain.  In  modem  elevators  for  heavy  purposes 
wrought-iron  links  connected  together  by  turned  bolts  passing  through  machine- 
bored  holes  are  almost  exclusively  employed. 

On  gasworks,  the  principal  materials  requiring  transport  from  one  point  to 
another  are  coal,  coke  (either  hot  or  cold),  clinkers,  and  in  some  cases  oxide  of  iron, 
lime,  and  such-like  materials.  It  is  chiefly,  however,  materials  of  moderately  high 

density  which  have  to  be  considered.  This 
fact  is  of  importance  in  that  it  has  an 
important  effect  upon  the  angle  of  slope 
of  the  elevators.  Machinery  dealing  with 
vegetable  matters  of  low  specific  gravity 

Floating  Pulley  s   N|N     '         ^X..        ^x      can  be  driven  at  very  much  higher  speeds 
(weighted*     \j  J  ^*\         than  that  made  use  of  for  such  substances 

as  coal.  Elevators  for  coal,  moreover, 
must  be  inclined  so  that  part  of  the  load 

FIG.  169.—  COMPENSATING  DEVICE  FOB  TAKING  is  borne  by  the  rubbing  strips  attached  to 
UP  SLACK  IN  DRAW-BAR  CONVEYORS  AND    ^  •  i  mr          11  •   i  .    • 

CHAINS  OR  ROPES.  the  gulde  supports.     The  whole  weight  is 


not  then  hanging  from  the  driving  sprocket, 

as  is  the  case  with  the  vertical  elevator.  For  heavy  materials  the  angle  of  slope 
(with  the  horizontal)  should  lie  between  45  and  60  degrees,  although  many  gasworks 
elevators  are  erected  at  so  great  an  angle  as  70  degrees,  or  in  some  cases  vertically. 
The  speed  should  not  exceed  130  feet  per  minute  under  any  circumstance.  In  the 
De  Brouwer  combined  hot  coke  elevator  and  conveyor  the  normal  working  speed  is 
in  the  neighbourhood  of  40  feet  per  minute,  and  the  angle  of  slope  is  usually  no  more 
than  30  degrees  with  the  horizontal.  It  is  necessary  to  bear  in  mind  that  when  a 
friable  material  such  as  coke  is  being  dealt  with  the  speed  of  an  elevator  of  the  bucket 
type  should  be  low,  because  a  high  velocity  of  delivery  entails  considerable  breakage 
of  the  material,  in  addition  to  curtailing  the  life  of  the  receiving  shoots.  In  general, 
it  may  be  said  that  coke  elevators  should  not  be  operated  at  a  greater  speed  than 
60  to  90  feet  per  minute.  Capacity,  usually  based  on  tons  delivered  per  hour, 
depends,  of.  course,  largely  on  speed,  but  also  upon  the  size  and  pitch  of  buckets,  or 
—in  the  draw-bar  types—  upon  the  depth,  width,  and  pitch  of  the  bars. 

With  bucket-conveyors  much  depends  upon  the  extent  to  which  each  bucket 
is  rilled.  Where  average  practical  conditions  are  considered,  the  following  formula 
may  be  taken  as  a  useful  guide  to  capacity  :— 

S  x  B  x  W, 

Capacity  =  —  tons  per  hour. 

yt>,  /DO  x  r 

where  B  =  Capacity  of  buckets  in  cubic  inches. 
S  =  Speed  of  conveyor  in  feet  per  minute. 
W.=  Weight  per  cubic  foot  of  substance  carried  (see  page  240). 
P  =  Pitch  of  buckets  in  feet. 


THE   MECHANICAL   HANDLING   OF   MATERIALS     207 


BAND  CONVEYORS 

Band  or  belt  conveyors  have  attained  a  certain  degree  of  popularity  on  gasworks, 
and  for  conveying  the  lighter  materials,  such  as  oxide  of  iron  or  sulphate  of  ammonia, 
they  are  probably  to  be  preferred  to  other  types.  For  such  materials  less  power  is 
required  by  a  band  conveyor  than  by  any  other,  and  the  speed  may  run  up  to  as 
much  as  600  feet  per  minute.  For  heavier  substances,  such  as  coal  and  coke,  the 
whole  design  must  necessarily  be  of  a  much  stiiTer  nature,  whilst  the  band  itself  must 
be  considerably  stronger  in  order  to  take  the  greater  weight 
imposed  upon  it.  It  is  not  generally  realized  that  when  used 
for  coals  the  centre  of  the  band,  and  not  the  outside  edges, 
shows  the  greatest  tendency  to  wrear ;  consequently  the 
middle  portions  of  the  width  require  special  care  in  their  pre- 
paration. In  a  general  way,  leather  material  as  used  for 
ordinary  driving  belts  is  to  be  avoided,  and  the  band  is  prefer- 
ably composed  of  special  insertion  covered  with  india-rubber 
where  it  comes  in  contact  with  the  rollers  or  guides.  The 


FIG.    170.— BAND    CON- 
VEYOR WITH  TROUGHED 
LEADING  PORTION. 


upper  portion  which  carries  the  load  should  be  made  from  solid,  india-rubber,  which 
may  be  reduced  in  thickness  towards  the  edges.  Canvas  or  balata  is  often  used. 

There  are  two  main  types  of  band  conveyors,  namely,  those  in  which  the  leading 
and  return  portions  of  the  belt  pass  over  parallel  guide  rollers  so  that  throughout 
its  travel  the  belt  is  perfectly  flat,  and  those  in  which  the  rollers  are  so  arranged 
as  to  cause  the  leading  portion  of  the  belt  to  assume  a  trough-like  shape  (Fig.  170). 

The  speed  of  band  conveyors  depends  largely  on  the  weight  of  the  material  to 
be  conveyed,  but  also  to  a  considerable  extent  upon  the  size  of  the  lumps.  So  far 
as  the  last-named  factor  is  concerned  the  rate  of  travel  should  vary  in  inverse  ratio 
to  the  size  of  the  pieces  ;  hence  large  lumps  must  travel  more  slowly  than  smaller 
ones.  Under  normal  conditions  the  speed  for  coal  purposes  wrill  be  from  150  to  300  feet 
per  minute,  although  with  fine  coal  this  may  be  increased  up  to,  400  feet  per  minute. 
The  following  table,  compiled  by  Zimmer,  gives  an  indication  of  the  capacity  of 
these  elevators  and  the  horse-power  required  to  drive  them.  The  author,  however, 
is  of  the  opinion  that  the  speed  given  (600  feet  per  minute)  is  too  great,  the  maximum 
figure  for  capacity  too  liberal,  and  the  B.H.P.  for  wider  buckets  not  adequate. 

SPEED  AND  CAPACITY  OF  BAND  CONVEYORS  FOB  COAL 


Width 
of 
band. 

Speed. 

Capacity. 

Size  of  coal. 

B.H.P.  for 

100  feet  length 
of  conveyor. 

Inches. 

12 

Feet  per  min. 
150  to  600 

Tons  per  hour. 
10  to  35 

From  2-inch  to  dust 

3-2 

18 
24 

» 

50  to  175                  „     4-inch  to  f-inch 
125  to  475                  „     6-inch  to  1-inch 

4-8 
6-0 

30 

250  to  900                  „     7-inch  to  2-inch 

7-6 

36 

350  to  1,500               „     9-inch  to  2-inch 

9-2 

208 


MODERN   GASWORKS   PRACTICE 


FIG.  171. — BELT  CONVEYOR  FOR  COAL. 

Band  conveyors  need  not  necessarily  be  operated  on  the  level,  but  can  also  be 
used  for  elevating  purposes.  When  conveying  up-hill,  however,  the  inclination 
should  not  be  greater  than  25  degrees,  otherwise  their  capacity  will  be 
reduced  by  slip.  When  the  band  is  inclined  the  power  necessarily  increases  in 
accordance  with  the  height  through  which  the  load  is  raised.  One  of  the  chief  advan- 
tages attached  to  this  type  of  conveyor  is  that  it  does  not  injure  in  any  way  the 
material  on  which  it  is  working. 


THE   MECHANICAL   HANDLING   OF   MATERIALS     209 


There  are  many  other  types  of  conveying 
machinery  in  more  or  less  general  use  on  gas- 
works, the  following  being  the  more  important 

systems  : — 

(a)  The  travelling-tray  conveyor. 
(6)  The  swinging-tray  conveyor. 

(c)  The  push-plate  conveyor. 

(d)  The  gravity-bucket  combined  eleva- 

tor and  conveyor. 

(e)  Telphers. 

TIPPING  OR  TRAVELLING-TEAY  CONVEYORS 

Band  conveyors  are  not  wholly  suitable 
for  conveying  substances  of  a  heavy  or  abra- 
sive nature,  on  account  of  the  injury  caused  to 
the  material  forming  the  belt.  Owing  to  the 
advantages  they  offer,  however,  conveyors 
embracing  the  principle  of  the  band  are  fre- 
quently preferred  by  many  engineers,  and  the 
travelling-tray  conveyor,  whilst  disposing  of  the 
perishable  belt,  retains  the  desirable  features 
of  the  system.  Figs.  172  and  173  illustrate 
one  of  the  best  known  types  of  travelling-tray 
conveyors.  This  type  of  conveyor  consists 
essentially  of  an  endless  chain  to  which  are 
attached  a  number  of  overlapping  trough-like 
sections.  The  chief  objection  to  the  employ- 
ment of  these  conveyors  is  their  inability  in 
many  cases  to  deliver  at  intermediate  points 
in  their  length.  In  the  type  illustrated,  how- 
ever, a  special  tip-up  bar  enables  the  conveyor 
to  deliver  at  any  desired  point  in  its  course,  or 
at  several  points  simultaneously,  as  well  as 
over  the  extreme  end.  By  a  simple  modifica- 
tion, moreover,  the  material  can  be  carried  up 
a  gradient  much  in  excess  of  the  limiting  angle 
of  the  material  on  the  trays.  In  discharging  a 
friable  material  such  as  coke  over  the  end,  the 
drop  is  minimized  by  the  preceding  tray  inter- 
cepting the  fall  of  material  from  the  tray 
following  it.  The  power  required  is  low  in 
comparison  with  types  of  conveyors  such  as 
the  push-plate,  and  is  usually  under  5  per  cent,  of  the  weight  of  the  moving  parts. 


"210 


MODERN   GASWORKS   PRACTICE 


About  250  feet  of  conveyor  carrying  20  tons  of  material  per  hour  can  be  worked 
with  one  indicated  horse-power.      When  the  conveyor  is  required  for  use   as   an 


elevator  back  lips  are  applied  to  the  trays.     The  normal  speed  of  travel  is  somewhat 
less  than  with  push-plate  conveyors,  and  varies  between  60  and  120  feet  per  minute. 


THE   MECHANICAL   HANDLING   OF   MATERIALS     211 

PUSH- PL  ATE  CONVEYORS 
A  typical  form  of  push-plate  conveyor  is  illustrated  in  Fig.  174.     Each  push- 


plate,  it  will  be  seen,  has  a  projecting  axle  at  either  end  to  which  special  rollers  are 
attached.     The  push-plates  are  secured  by  special  chain  attachments,  and  discharge 


212 


MODERN   GASWORKS   PRACTICE 


outlets  with  side  doors  are  fixed  at  convenient  intervals.  Conveyors  operated  on 
this  principle  may  be  arranged  with  either  a  single  or  double  chain,  but  in  any  case 
the  push-plates  should  not  be  allowed  to  touch  the  bottom  of  the  trough.  For  this. 
reason,  in  those  designs  where  guided  rollers  are  not  made  use  of,  the  plates  are  fitted 
with  some  form  of  skidder-bar  which  slides  in  its  guides  and  takes  the  greater  portion 
of  the  wear.  So  far  as  economy  in  motive  power  is  concerned  the  roller  types  are 
to  be  preferred.  The  normal  speed  of  these  conveyors  is  somewhat  greater  than 
that  of  the  tipping- tray  type,  and  varies  between  60  and  180  feet  per  minute.  The 
capacity  depends  upon  the  speed,  the  size  of  the  trough,  and  the  pitch  of  the  draw- 
bars. The  pitch  may  be  anything  from  18  inches  to  3  feet.  With  the  usual  trough 
of  about  2  feet  in  width  and  having  push-plates  at  a  pitch  of  2  feet  the  capacity  is 
normally  30  tons  per  hour,  with  an  average  speed  of  100  feet  per  minute.  Conveyors 
of  this  type  have  been  somewhat  generally  adopted  for  the  removal  of  hot  coke  from 
retort  houses.  When  used  for  this  purpose  it  must  be  borne  in  mind  that  the 
friability  of  the  coke  will  not  permit  of  a  high  rate  of  travel,  if  disintegration  of 
the  material  is  to  be  avoided.  In  the  De  Brouwer  conveyor  the  average  rate  of 
travel  does  not  exceed  40  feet  per  minute. 

GRAVITY-BUCKET  CONVEYOR 

The  gravity-bucket  or  travelling-bucket  conveyor  has  for  some  years  been  a 
foremost  favourite  in  America,  and  is  now  assuming  some  considerable  importance 
in  this  country.  Briefly  described,  it  consists  of  two  endless  chains  held  apart  at 


FIG.  175. — THE  GRAVITY -BUCKET  CONVEYOR. 


a  pre-determined  distance  by  suitable  bars,  to  each  end  of  which  is  fixed  a  small 
roller,  these  rollers  running  along  special  guide-tracks.  The  distance  pieces  between 
the  chains  are  fitted  with  buckets  which  are  suspended  from  a  point  above  their 


THE   MECHANICAL   HANDLING   OF   MATERIALS     213 

centre  of  gravity,  and  are  free  to  swing.  Thus,  whatever  the  position  of  the  endless 
chain,  the  buckets  always  hang  in  an  upright  position  whether  they  are  travelling 
vertically  or  horizontally.  For  this  reason  the  gravity- bucket  system  may  be  em- 
ployed to  perform  the  combined  duties  of  elevator  and  conveyor.  Delivery  at  any 
desired  point  is  arranged  for  by  interposing  a  device  which  tilts  the  bucket  and  dis- 
charges its  contents.  The  driving  gear  is  unique,  and  usually  consists  of  a  spur- 
geared  engine  operating  two  sets  of  panels  which  successively  thrust  the  chain  in 
the  direction  of  its  travel,  engaging  with  both  sides  simultaneously.  In  this  way 
the  chain  is  pushed  forward  link  by  link.  An  essential  feature  of  the  system  is  the 
provision  of  some  type  of  filling  device,  so  that  the  material  may  be  delivered  to  the 
buckets  without  undue  spilling.  The  filler  consists  of  a  hollow  casting  securely  keyed 
on  a  steel  spindle.  The  casting  is  formed  with  five  openings  in  its  periphery,  and 
these  are  arranged  to  centre  with  the  buckets  as  the  filler  is  rotating.  The  filler  is 
driven  direct  by  the  conveyor  chain  engaging  with  an  adjustable  sprocket  wheel 
bolted  on  the  rotating  hollow  casting.  The  speed  of  the  gravity  bucket  is  necessarily 
low,  the  rate  of  travel  normally  varying  between  25  and  50  feet  per  minute.  The 
capacity  depends  upon  the  size  and  speed  of  the  buckets  used,  and  installations  may 
be  erected  capable  of  handling  from  20  to  ICO  tons  and  upwards  per  hour.  The 
power  required  is  low  in  comparison  with  many  other  types  of  conveyor,  but  depends 
largely  upon  the  proportion  of  elevating  work  which  is  performed  (see  page  224). 

HOT-COKE   CONVEYOKS 

Owing  to  its  hard,  gritty,  and  abrasive  nature  coke  is  a  very  different  material 
irom  coal  with  which  to  deal,  and  unless  the  apparatus  used  for  handling  it  is  suitably 
designed  the  wear  and  tear  is  very  great.  This  is  particularly  the  case  when  the 
highly  heated  coke  has  to  be  dealt  with  as  it  is  discharged  from  the  retorts.  At  the 
present  day  there  are  two  principal  methods  of  dealing  mechanically  with  hot  coke  : — 

(1)  By  means  of  conveyors  of  the  push-bar  or  travelling- tray  types. 

(2)  By  means  of  transporters  or  telphers. 

Each  method  has  its  particular  advantages,  and  the  question  as  to  which  shall 
be  adopted  must  be  decided  entirely  by  local  conditions  and  requirements.  In  many 
cases  a  combination  of  the  two  types  is  the  ideal  arrangement,  a  conveyor  being 
used  inside  the  retort  house  and  a  telpher  outside  in  the  coke  yard.  Telphers  are 
not  solely  confined  to  dealing  with  coke,  and  are  now  extensively  used  for  coal  trans- 
portation as  well,  whilst  in  medium-sized  works  the  combined  duties  may  be  carried 
out  by  the  one  machine.  The  principal  advantages  of  a  telpher  plant  are  the  amount 
of  ground  which  can  be  covered  without  an  excessive  expenditure  and  the  small 
amount  of  handling  received  by  the  coke,  with  a  corresponding  decrease  in  the  pro- 
duction of  breeze.  Telphers  in  general  are  cheaper  than  hot -coke  conveyors,  and 
the  latter  are  certainly  offenders  with  regard  to  breakage  of  coke.  The  great  advan- 
tage of  the  conveyor,  however,  is  that  it  is  continuous  in  action,  and,  therefore,  does 
not  restrict  the  speed  of  the  stoking  machinery.  Moreover,  when  once  started  to 
work  it  is  practically  automatic  in  action,  and  does  not  require  a  man  in  constant 


214 


MODERN   GASWORKS   PRACTICE 


attendance  as  does  the  telpher.     The  cost  of  upkeep  of  the  telpher  is  light  in  com- 
parison with  conveyors. 

THE  DE  BROUWER  HOT-COKE  CONVEYOR 

This  type  of  hot-coke  conveyor  (illustrated  in  Fig.  176)  has  probably  been 
adopted  more  extensively  than  any  other  system,  both  in  this  country  and  on  the 
Continent.  On  English  gasworks  alone  more  than,  seven  miles  of  the  conveyor  are 
in  operation.  The  conveyor  consists  of  a  trough  of  varying  width  and  depth,  to  suit 
the  quantity  of  coke  to  be  dealt  with,  in  which  the  chain  slides.  This  trough  usually 
consists  of  a  J-inch  or  |-inch  steel  bottom  plate  with  steel  channels  or  angles  riveted 
along  each  side,  the  joints  being  made  so  as  to  form  a  watertight  pan  in  which  are 
placed  cast-iron  renewable  bottom  plates.  These  bottom  plates  are  about  f-inch 


FIG.  176. — THE  DE  BROUWER  HOT-COKE  CONVEYOR. 

thick  in  the  middle  with  raised  paths  -f  inch  deep  on  each  side  for  the  chains  to  slide 
upon.  The  chains  are  protected  by  steel  angles  or  tees  bolted  to  the  trough  sides 
with  special  countersunk  headed  bolts.  The  sides  of  the  trough  are  protected  by 
|-inch  steel  renewable  plates  which  are  bolted  on  with  countersunk  headed  bolts. 
These  plates  also  hold  the  cast-iron  bottom  plates  in  position.  In  some  cases  the 
trough  in  the  retort  house  is  covered  over  with  hinged  doors  of  J-inch  or  ^-inch  steel 


THE   MECHANICAL   HANDLING   OF   MATERIALS     215 

chequered  plate,  level  with  the  floor,  the  doors  on  the  retort  bench  side  being  used 
to  deflect  the  coke  from  the  retorts  into  the  trough.  After  leaving  the  retort  house 
the  conveyors  usually  rise  at  an  angle,  varying  with  the  space  available,  to  a  suitable 
height  for  delivering  the  coke  into  hoppers,  etc.  In  these  cases  the  trough  up  the 
slope  is  made  about  2  feet  deep  by  means  of  ^-inch  steel  side  plates  and  is  covered 
by  y^-inch  steel  plates  bolted  on  the  top,  thus  completely  enclosing  the  trough  and 
carrying  the  steam  from  the  quenching  to  a  steel  chimney  near  the  top  of  the  incline. 


FIG.  177. — WEST'S  HOT-COKE  CONVEYOR. 


By  this  means  the  steam  is  kept  in  contact  with  the  coke  for  a  considerable  time  and 
ensures  the  coke  being  properly  quenched.  .  The  quenching  sprays  are  fixed  to  the  top 
plate  over  the  trough  near  the  bottom  of  the  slope,  the  surplus  water  draining  out 
through  a  grid  fixed  to  the  trough  side  on  the  level  portion  near  the  bend.  Guide 
rollers  or  wearing  blocks  are  fitted  at  the  bend  to  prevent  the  chains  rising  out  of 
the  trough,  the  angle  of  the  incline  deciding  which  shall  be  used.  The  return  path 
for  the  chains  usually  consists  of  steel  angles  with  cast-iron  renewable  wearing  strips 
bolted  on  with  countersunk  headed  bolts,  supported  either  under  or  over  the  trough 
as  is  most  convenient.  The  chain  consists  of  best  steel  stamped  block  links  (except 


216 


MODERN  GASWORKS  PRACTICE 


where  the  cross-bars  come,  these  being  of  cast  steel,  cast  solid  with  the  cross-bars), 
alternating  with  double  links,  the  block  links  being  made  specially  high  to  take  all 
the  wear  due  to  the  rubbing  on  the  wearing  strips  of  the  pan.  The  side  links  are 
connected  in  such  a  manner  that  the  wear  comes  upon  the  full  width  of  the  portion 
passing  through  the  hole  in  the  block  link  and  they  are  held  together  by  rivets,  which 
are  made  easy  of  removal  while  being  perfectly  secure  and  forming  no  part  of  the 
wearing  surface.  The  two  chains  are  held  apart  by  2  J  inches  by  \  inch  flat  cast-steel 


FIG.  178. — DEMPSTER'S  HOT-COKE  CONVEYOR. 

bars  cast  solid  with  the  block  links  at  intervals  of  2  feet  1£  inches,  for  the  trans- 
mission of  the  coke  along  the  conveyor.  The  conveyor  is  driven  by  cast-iron  wheels 
fitted  with  renewable  manganese  steel  sprockets,  and  at  each  bend  passes  round  cast- 
iron  flanged  rollers.  Suitable  tension  gear,  as  described  on  page  206,  is  provided  for 
taking  up  any  extension  of  the  chain.  A  chain  of  the  De  Brouwer  type  will  deal  with 
from  50,000  to  60,000  tons  of  coke  during  its  working  life.  The  speed  of  travel  of 
the  conveyor  is  low,  averaging  about  40  feet  per  minute. 

A  somewhat  similar  type  of  hot-coke  conveyor,  but  one  in  which  a  different  type 


THE   MECHANICAL   HANDLING   OF   MATERIALS      217 

-of  chain  is  employed,  is  shown  in  Fig.  177.  Dempster's  hot-coke  conveyor  is  another 
familiar  pattern.  As  will  be  seen  from  Fig.  178,  it  is  of  the  rake  type,  and  is  so 
arranged  that  only  the  rakes  are  in  contact  with  the  coke,  all  the  moving  parts  being 
on  an  elevated  pathway  and  screened  from  the  coke  by  means  of  baffle  plates.  Thus 
the  chains  and  sliding  shoes  are  clear  of  both  coke  and  quenching  water.  The  trough 
is  formed  of  channels  and  Z-steel  sides  with  steel  bottom  plate.  The  inside  of  the 
trough  is  provided  with  cast-iron  liners  and  steel  flat-bars  on  the  Z-sections  for  the 
chain  shoes  to  run  on.  As  in  the  other  types  of  conveyors  the  return  can  be  arranged 
overhead  if  so  desired.  The  chains  are  entirely  formed  of  low  carbon  steel  to  prevent 
corrosion  by  acid  fumes,  etc.,  evolved  by  the  coke  during  quenching.  The  rakes 
are  of  malleable  iron,  and  the  sliding  shoes  of  chilled  cast-iron. 

DRAKE'S  TRAY  CONVEYOR 

This  hot- coke  conveyor  is  unique  in  that  it  embraces  the  principle  of  carrying 
the  coke  and  not  dragging  it.  The  general  construction  is  shown  in  Fig.  179,  from 
which  it  will  be  seen  that  the  conveyor  consists  of  corrugated  trays  mounted  on 
wheels,  and  running  in  a  cast-iron  trough.  There  is  in  reality  no  wearing  part  with 


FIG.  179. — DRAKE'S  TRAY  HOT-COKE  CONVEYOR. 


the  exception  of  the  wheels,  which  revolve  upon  a  fixed  pin.  The  connexion  between 
the  trays  is  also  by  a  pin,  wHich  acts  as  an  axle  when  the  trays  are  running  round 
the  drum,  ready  for  the  return.  The  trough  is  fitted  with  curtain  plates  which  over- 
lap the  inside  of  the  tray  and  which  prevent  the  coke  from  getting  over  the  side  and 
into  the  path  of  the  wheels. 

TELPHER  TRANSPORTERS 

Transporters  operating  on  the  telpher  principle  are  of  comparatively  recent 
introduction,  having  been  first  installed  in  this  country  by  Siemens  Brothers  in 


218 


MODERN   GASWORKS   PRACTICE 


1903.  There  is  no  doubt  that  they  are  destined  to  play  a  prominent  part  in- 
gasworks  methods  of  the  future.  Their  construction  is  too  simple  to  need  any 
detailed  description  here.  The  illustrations  will  best  explain  the  chief  features. 
The  machine  is  provided  with  a  cabin,  in  which  the  driver  sits,  and  is  driven  by  two 
electric  motors,  one  for  travelling  and  the  other  for  hoisting.  In  the  most  common 


Trolley  Wire 


Travelling  Brake 


Travelling  Motor 


Travelling  Carriage 


•   Cab  Light 


Sliding  Pinion 
Hand  Lever  . 


Sliding  Door 
Electric  Controller 


FIG.  180. — STANDARD  TELPHER  CARRIAGE  (STRACHAN  &  HENSHAW'S  TYPE). 


types  (Figs.  180  to  183)  the  travelling  motor  is  of  about  6  h.p.,  and  the  hoisting 
motor  12  h.p.,  for  a  machine  of  about  35  cwt.  gross  capacity.  The  power,  of 
course,  varies  with  the  load  to  be  dealt  with  and  the  speed  required.  The  whole 
machine  travels  along  a  single  track  usually  formed  of  a  stiff  joist  with  a  rail 
section  bolted  to  the  upper  flange.  The  two  bogies  on  which  the  carriage  is 
supported  are  pivoted  to  allow  the  machine  to  traverse  curves  of  small  radius  r 


and  in  some '  cases  they  are  made  to  run  on  the  bottom  flange  of  the  track 
girders  instead  of  along  a  rail.  Telphers  are  largely  used  for  handling  both 
coal  and  coke,  and  machines  have  been  built  to  take  loads  up  to  4  or  5  tons 
at  a  speed  of  80  feet  per  minute.  In  such  cases  the  lifting  motor  would 
be  from  35  to  40  h.p.  The  system  of  dealing  with  hot  coke  direct  from  the 
retorts  by  means  of  lattice  or  bar  skips  attached  to  the  hauling  wire  is  probably 


FIG.  181. — TELPHER  AND  TRACK." 


one  of  the  most  ideal.  The  coke  is  discharged  from  the  retort  direct  into  the  skip, 
which  is  hauled  up,  conveyed  from  the  retort  house,  and  lowered  into  a  tank  of 
water  for  quenching  purposes.  When  quenching  is  complete  the  skip  is  raised 
from  the  tank,  and  the  coke  is  automatically  deposited  at  the  required  spot  in  the 
store  yard.  In  the  quenching  of  coke  in  this  manner  it  is  advantageous  to  permit 
as  much  of  the  cooling  as  possible  to  be  performed  by  the  escaping  steam ;  hence 


•220 


MODERN   GASWORKS   PRACTICE 


only  the  lower  portions  of  the  skip  should  be  submerged.  Wear  and  tear  is  con- 
siderably minimized  with  electric  telphers,  as  the  only  portion  of  the  apparatus  in  con- 
tact with  the  heated  coke  is  the  skip,  wrhich — with  minor  repairs — should  last  a 
number  of  years.  The  average  machine  handles  gross  loads  of  2  tons  with  a  hoisting 
speed  of  80  to  100  feet  per  minute,  according  to  the  height  of  the  hoist,  whilst  a 
travelling  speed  of  from  400  to  750  feet  per  minute,  according  to  the  length  of  run, 
may  be  attained.  This  is  ten  to  twenty  times  as  great  as  the  speed  of  the  ordinary 
hot-coke  conveyor. 


FIG.  182. — ELECTRIC  TELPHER  WITH  COKE  SKIP. 


Probably  the  most  satisfactory  arrangement  of  trackwork  is  the  method  by 
which  the  telpher  track  is  suspended  from  overhead  steel  lattice  girders,  these  girders, 
having  spans  of  from  60  to  100  feet,  being  supported  at  the  ends  by  steel  trestles. 
'This  arrangement  gives  the  least  possible  number  of  obstructions  in  the  yard,  and 
there  are  fewer  trestles  to  suffer  from  the  corrosive  action  of  the  coke  mass  surround- 
ing them.  It  is  preferable  in  all  cases  where  uprights  are  likely  to  be  buried  in  coke 
-.to  concrete  these  up. 

The  telpher  collects  its  current  from  an  overhead  trolley  wire  attached  to  insu- 


221 


1222 


MODERN   GASWORKS   PRACTICE 


lators  above  the  track.  A  single  wire  is  quite  suitable  when  the  engineer  is  able 
to  utilize  current  which  is  generated  at  the  works,  as  an  earth  return  is  then  per- 
missible, but  in  cases  where  current  is  taken  from  the  town's  mains  two  lines  should 
be  used,  a  positive  and  negative,  so  as  to  avoid  the  earth  return.  With  regard 
to  skips,  which  are  the  main  renewable  items,  these  cost  about  £30  each,  for  a  capacity 
of  1  ton. 

It  may  be  pointed  out  that  Continental  practice  favours  the  automatic  tel- 
pher, that  is  a  machine  with  which  no  man-handling  is  required.  Such  machines 
are  controlled  by  electrical  means  from  a  fixed  station.  On  the  Continent  the 
man-handled  telpher  is  looked  upon  as  somewhat  old-fashioned  and  wasteful ;  but, 
on  the  other  hand,  the  automatic' plant  introduces  electrical  complications  which 
are,  perhaps,  best  avoided  in  conditions  such  as  obtain  on  gasworks.  Very  much 
more  skilled  attention  is  required,  and  when  .a  breakdown  occurs  it  is  usually 
more  difficult  to  deal  with. 


THE  COST  OF  CONVEYORS 

In  order  to  compare  the  relative  costs  of  conveying  machinery  it  is  necessary 
to  base  figures  on  equivalent  capacities  for  the  different  types  in  question.  In 
general,  costs  are  based  on  the  outlay  per  foot  run.  Thu^  the  total  length  of  the 
installation  has  some  influence  on  this  item.  The  following  table  gives  average 
figures  prevailing  in  normal  times,  and  should  prove  useful  for  purposes  of 
comparison  : — 

•(1)  De  Brouwer  hot-coke  type      .          .         .          .          .          .          .      £4  to  £5  per  foot  run. 

(Yard  conveyors  supported  at  a  considerable  height  above  the  ground  may  entail  an  outlay 
of  £6  per  foot,  which  includes  supports.) 


Travelling-tray  hot-coke  conveyor  (Drake's  type) 


£5  per  foot  run. 


s. 


8.    d. 


4  3)  Gravity- bucket  conveyors —  £ 

(a)  Capacity  25  tons  per  hour  .         >         .         .20 

(6)          „        30           „  ...          .25 

(c)  ,',        50           „         „  . .          .          .  '       .     2  10 

(d)  ,,80          „  ....     3     0 

(e)  „       100           „  .3  10 

(The  above  prices,  for  an  average  length  of  250  feet,  include  the  chain,  buckets,  wheel  curves 
track  rail,  fillers,  vertical  guides,  etc.,  but  not  the  motor  for  driving.) 


d.        £ 

0  to  2     5     0  per  foot  run. 
0    „   2  10     0 
0    „   2  15     0 
0    „   3  10     0 
0 


0 


4     0 


1(4)  Push- plate  conveyors  for  coal— 

(a)  Capacity  20  tons  per  hour 
(6)         „        25-30     „ 

(c)  „        35-40     „ 

(d)  „        50 


£    s.  d.        £    s.  d. 

3     5  0  to  3  10  0    per  foot  run. 

3  10  0    „   3  15  0 

3  15  0    „   4    0  0 

4  0  0    „   4    5  0 


(Conveyor  complete,  with  exception  of  driving  motor.) 


223 


224 


MODERN   GASWORKS   PRACTICE 


(5)  Tipping-tray  conveyors  for  coal — 

(a)  Capacity  50  tons  per  hour          .    , 

(b)  „        80 

(c)  „      100 

(6)  Bucket  elevators — 

(a)  Capacity  25-30  tons  per  hour    . 

(b)  „  .45 

(c)  „  55  „         „        . 

(7)  Telphers — 

Track  and  trolley  wire. 

Telpher  and  motors  (each)    . 

Skips  for  coke  (each),  1  ton  capacity 


£    s.  d.        £  s.  d. 

6  10  0  to  7  0    0  per  foot  run- 

7  0  0    „   7  5     0 
7  10  0    „   8  0    0 


£    s.  d. 
4  15     0  to 

6     0    0  to 


£    s.  d. 

500   per  foot  run. 

5  10     0 

6  10    0 

£    s.  d. 

3  10    0  per  foot  run. 

about  £500. 

£30. 


THE   CALCULATION   OF   HORSE-POWER 

The  power  necessary  to  drive  the  various  types  of  elevators  and  conveyors  has 
in  many  cases  been  arrived  at  by  practical  experience  and  reference  to  the  makers' 
records.  It  is,  however,  useful  to  be  able  to  form  an  opinion  as  to  the  likely  horse- 
power which  will  be  required  by  any  one  installation,  and  the  following  simple  but 
reliable  methods  will  probably  prove  of  some  assistance  to  the  designer. 

First,  in  the  case  of  conveyors  such  as  the  gravity-bucket  and  tipping- tray 
types,  practical  experience  has  shown  that  the  tractive  force  is  rather  under  5  per 
cent,  of  the  total  weight  of  the  moving  parts  and  load.  In  addition  to  this  100  per 
cent,  should  be  allowed  for  contingencies,  such  as  neglect  of  lubrication  and  general 
inefficiencies.  A  gravity-bucket  almost  invariably  performs  two  functions,  first 
conveying  horizontally,  and  secondly  elevating  the  material.  It  therefore  requires 
an  operating  power  for  a  subdivision  of  these  functions,  namely  : — 

A.  Driving  the  empty  conveyor. 

B.  Carrying  and  elevating  the  material. 

The  calculation  for  operating  power  is  therefore  most  easily  made  in  three 
sections  : — 

(1)  The  power  to  operate  the  empty  conveyor. 

(2)  The  power  to  operate  the  load. 

(3)  The  power  to  raise  the  load. 
To  formulate  this — 

Let  L    =  length  of  conveyor  chain  in  feet. 
,,    W  =  weight  per  foot  run  of  conveyor  in  pounds. 
,,    I     =  length  of  conveyor  loaded  per  foot. 
,,    T    —  capacity  in  tons  per  hour. 
,,    S    =  speed  in  feet  per  minute. 
,,    H  =  height  to  which  material  is  to  be  elevated. 

Then  the  total  weight  of  conveyor  and  moving  load  (in  pounds)  is  given  by  the 
formula — 

JTX2240 
S  X60 


THE   MECHANICAL  HANDLING   OF  MATERIALS     225 

The  result  of  the  above  formula  gives  the  total  weight  in  pounds  of  the  moving 
parts,  and  10  per  cent,  of  this  would  be  taken  as  the  maximum  pull  (P)  or  driving 
effort  on  the  chain  of  the  conveyor.      Kesolving   this   into   horse-power  we  get  — 
PS 

~  ^or  ckanl  anc^  l°ad  exclusive  of  the  power  required  to  lift  the 

material  through  a  height. 

The  horse-power  for  lifting  is  represented  by  the  formula  — 


j  TW   ,  ZTx2240  , 

H.P.  =  -     -  ,  where  Wj  =  LW  +  --  (as  above). 
33,000'  S  x  60 

Adding  the  two  results  together  gives  the  total  power  necessary  for  the  driving 
motor.  In  a  horizontal  conveyor,  of  course,  the  second  formula  is  eliminated. 
The  calculation  for  tipping-tray  conveyors  can  be  carried  out  in  the  same  manner. 

As  regards  conveyors  of  the  De  Brouwer  hot-coke  pattern  it  is  customary  to 
allow  about  1  horse-power  for  40  feet  run,  and  when  the  coke  is  taken  up  an  incline 
the  additional  power  entailed  in  raising  the  load  must  be  added.  The  latter  may 
be  readily  calculated  as  explained  above.  In  all  cases  where  the  expression  "  foot 
run  "  has  been  used  in  this  chapter,  it  refers  to  foot  run  of  conveyor  and  not  to  the 
length  of  chain  employed. 

The  horse-power  required  may  also  be  readily  arrived  at  by  adopting  a 
coefficient  of  friction  in  accordance  with  the  conditions  upon  which  the  elevator 
is  operated.  The  various  cases  would  then  be.  treated  in  the  following  manner  :  — 

(a)  Vertical  elevator. 

Let  M  =  weight  of  material  carried  in  pounds. 
W  =  weight  of  moving  parts  in  pounds. 
K  =  coefficient  of  friction  (see  below). 
S    =  speed  per  minute  in  feet. 

Hp         MS        KS  (M  +  W) 

33,000  33,000 

(6)  Inclined  elevator. 
Let  0  =  angle  of  inclination  with  horizontal. 

Hp     _  MS  Sin  0       KS  (M  +  W)  Cos  0 

33,000  33,000 

(c)  Horizontal  conveyor. 


H.P.  = 


KS  (M  +  W) 


33,000 
So  far  as  the  value  of  K  is  concerned  the  following  figures  may  be  taken  : — 

Metal  sliding  on  metal     .          .          .         f          .     '    .          .          .          .     0-15. 

Ditto,  well  lubricated        .          .      ^  .'         .          .          .'•-..'         .          .     0-07  to  0-08. 

Wood  sliding  on  wood      .          .          .          ,  "  '    .         .         .          .          .     0-25. 

The  following  table  (Zimmer)  gives  a  comparison  between  the  relative  power 


226  MODERN   GASWORKS   PRACTICE 

absorbed  by  various  types  of  elevators  and  conveyors.     In  each  case  the  conveyor 
is  assumed  to  be  of  50  tons  per  hour  capacity,  and  to  have  an  effective  length  of 

100  feet  :— 

H.P. 

Band  conveyor  for  light  materials     .  ,         .         .         .  ;.     4-8. 

„  „  „     coal  .          .          .  ....          .          .          .     5-0. 

Swinging  conveyor  .         .         ^         .'  .  .     5-0  to  8-0. 

Push-plate  conveyor          ...  .    12-8. 

Worm  conveyor  .    •  •   18-38. 

Tubular  worm  conveyor  .         .         >  .         .         .         .         .         .25-0. 


CHAPTER   IX 
ELECTRICAL   PLANT   IN  GASWORKS 

THE  growing  use  of  electricity  as  a  source  of  power  for  operating  gasworks  plant 
has  rendered  a  knowledge  of  this  form  of  energy  of  increasing  importance.  A 
close  acquaintance  with  the  details  of  technical  electricity  is  by  no  means  jaecessary, 
for  the  practical  construction  of  the  apparatus  is  in  the  hands  of  specialists.  Every 
gas  engineer  should,  however,  aspire  to  a  working  knowledge  of  the  subject  and 
be  in  touch  with  the  applications  in  practice  of  the  more  important  theories.  The 
importance  of  electricity  has  recently  been  emphasized  by  instances  where  gas 
concerns  have,  in  addition,  obtained  powers  for  a  public  supply  of  current. 

If  electrically  driven  charging  machinery  is  in  use  it  is  obviously  economical 
in  the  majority  of  cases  to  operate  other  coal  and  coke-handling  plant  by  the  same 
means.  As  a  general  rule  it  may  be  said  that  the  ideal  conditions  for  all  power 
consumers  is  the  continuous  use  of  a  set  of  plant  working  at  something  approaching 
its  normal  maximum  capacity.  To  this  end,  it  can  usually  be  arranged  to  work 
the  coal-handling  plant  together  with  charging  machinery  for  ten  or  twelve  hours 
out  of  the  twenty- four,  and  the  charging  machinery  during  the  night  only.  In  small 
works  it  is  possible  to  make  use  of  the  coal-handling  and  charging  machinery  alter- 
nately with  the  same  power  installation,  and  in  this  way  the  necessary  electrical 
plant  is  considerably  reduced.  If  coke  conveyors  are  also  installed  it  can  be  arranged 
to  use  two  out  of  the  three  pieces  of  plant  at  one  time. 

Electricity  when  generated  by  means  of  town  gas  is  an  extremely  cheap  form 
of  power,  particularly  when  it  is  used  on  gasworks,  for  in  such  cases  the  gas  con- 
sumed should  be  reckoned  on  "  cost  into  holder  "  figures.  In  comparing  costs  with 
those  of  steam-driven  generating  plant  the  expense  entailed  in  the  provision  of 
boilers  should  be  included.  If,  however,  existing  excess  boiler  power  is  available, 
then  generation  by  steam  has  its  attractions.  Steam,  moreover,  may  be  pro- 
duced by  means  of  materials  which  may  frequently  be  almost  unsaleable.  In 
general,  however,  preference  should  always  be  given  to  generation  by  gas,  unless 
other  methods  present  indisputable  advantages. 

DIRECT   OR  ALTERNATING   CURRENT 

In  gasworks,  where  the  current  has  to  be  transmitted  only  a  very  short  distance, 
the  most  suitable  system  of  supply — and  that  in  common  use — is  the  direct  current. 
The  advantages  gained  by  the  introduction  of  the  multi-phase  alternating  system 

227 


228  MODERN   GASWORKS   PRACTICE 

(i.e.  the  transmission  of  high  power  through  small  cables  and  with  little  loss  over  a 
long  distance)  are,  therefore,  of  no  material  account.  Furthermore,  the  nature  of 
the  requirements  of  the  various  units  to  be  driven  does  not  call  for  the  peculiarities 
of  the  alternating  system.  In  fact,  the  starting  torque  of  direct  current  is  preferable 
with  the  majority  of  the  motors  employed.  The  alternating  current  demands  more 
skilled  attention,  and  there  is  greater  liability  to  personal  danger  than  with  the 
direct  system.  The  most  common  pressure  in  use  is  220  volts. 

Once  the  system  of  supply  and  the  motive  power  for  the  generators  has  been 
decided  upon  the  type  and  size  of  plant  should  be  considered.  For  small  and  medium- 
sized  installations  the  standard  horizontal  single  cylinder  gas  engine  is  to  be  recom- 
mended, the  electric-lighting  type  being  specially  built  for  this  class  of  work.  For 
very  large  sets  the  vertical  high-speed  engine  with  two  or  more  cylinders  is  more 
effective.  There  are  two  methods  of  driving  the  dynamo  : — 

(a)  By  belting. 

(&)  Direct  drive  by  means  of  a  flexible  coupling. 

Method  (a)  accounts  for  a  small  waste  of  power,  but  carries  the  advantage  that 
the  speed  of  the  generator  may  be  greater  than  that  of  the  engine.  Accordingly,  for 
the  same  power  a  smaller  generator  may  be  used.  The  direct- coupled  machine  will, 
however,  last  longer  (owing  to  its  slower  running  speed),  is  safer  (owing  to  the  absence 
of  moving  belts),  and  occupies  less  ground  space.'  Taking  all  points  into  considera- 
tion, it  will  usually  be  found  that  a  direct  drive — in  spite  of  the  slight  extra  expense 
incurred — is  preferable,  and  of  more  lasting  economy.  The  engine  employed  should 
be  fitted  with  a  magneto  ignition  and  self-starter,  except  in  the  case  of  very  small 
units. 

THE  DYNAMO 

A  dynamo  is  a  machine  for  converting  mechanical  into  electrical  energy.  The 
mechanical  energy  supplied  induces  current  in  the  armature  windings,  the  current 
being  collected  by  brushes  and  passing  out  for  distribution  to  the  switchboard.  A 
small  portion  of  the  current  is  shunted  through  the  field  coils  for  magnetizing  the 
field.  The  armature  windings  generate  alternating  current,  and  the  commutator 
passes  this  out  as  a  current  of  continuous  flow  (i.e.  direct).  Thus  an  alternating 
current  dynamo,  or  "  alternator,"  has  no  commutator.  It  is  preferable  when 
installing  a  gasworks  dynamo  to  arrange  for  one  having  both  series  and  shunt  wind- 
ings (compound),  as  this  ensures  a  constant  voltage  for  all  variations  of  the  load — 
this  consideration  being  one  of  chief  importance.  The  field  regulating  switch  can 
be  fixed  either  in  series  or  parallel  (or  both)  with  the  field  coils.  In  practice,  how- 
ever, it  is  usually  fixed  on  the  shunt  coils,  as  this  permits  of  the  adoption  of  a  smaller 
rheostat,  owing  to  the  former  not  having  to  take  the  full  load  as  do  the  series  coils. 

SIZE   OF  THE   INSTALLATION 

With  regard  to  the  size  of  the  installation  to  be  laid  down  it  should  be  kept 
in  mind,  first,  that  it  is  necessary  to  arrange  for  more  than  a  single  plant,  and,  secondly, 
that  it  is  not  economical  to  work  a  set  at  much  less  than  its  normal  capacity.  In 


ELECTRICAL   PLANT   IN   GASWORKS  229 

large  works  the  night  load  is  much  smaller  than  the  day  load,  as  little  work,  except 
that  entirely  inside  the  retort  house,  is  carried  out  at  night.  In  medium-sized  works 
the  difference  in  load  may  not  be  very  great  and,  as  already  pointed  out,  in  small 
works  the  load  curve  may  be  very  nearly  straight.  In  the  last  named  case  it  is  advan- 
tageous to  instal  duplicate  plant,  each  set  being  capable  of  dealing  with  the  maximum 
load.  In  some  instances,  where  the  difference  between  the  day  and  night  load  is 
great,  it  may  be  preferable  to  have  two  plants  of  capacities  equal  to  each  period, 
with  a  stand-by  equal  to  the  lower  capacity.  Then,  if  the  smaller  unit  breaks  down 
there  is  a  duplicate  to  take  its  place,  and  if  the  larger  one  requires  repairs  there  will 
be  two  small  sets  for  providing  the  power.  It  must  be  remembered,  however,  that 
two  small  sets  such  as  these  could  not  be  run  in  parallel  without  special  arrange- 
ments on  the  switchboard;  otherwise  the  slightest  difference  in  voltage  would  mean 
the  slipping  of  current  from  one  dynamo  to  the  other.  The  best  arrangement  would 
be  to  depute  one  of  the  sets  to  driving  the  charging  machinery,  and  the  second  could 
provide  for  the  wants  of  the  coal  and  coke- handling  plant.  With  separate  circuits 
and  an  arrangement  of  change-over  switches  either  plant  could  be  transferred  to  the 
other's  work. 

A  TYPICAL  EXAMPLE 

Consider  a  works  carbonizing  about  200  tons  of  coal  per  diem,  and  having 
from  130  to  150  retorts.  The  larger  number  would  represent  the  normal  maximum 
work  of  a  combined  charger-discharger,  or  two-thirds  the  work  of  separate  machines. 
For  the  purpose  of  the  example  it  can  be  assumed  that  the  maximum  power  required 
by  the  machine  is  18  h.p.  The  necessary  motors  would,  therefore,  be  on  lines  such 
as  the  following  : — 

B.H.P. 
Charging  machinery        .  ,          .          .          .          .          .          .          .         ,.18 

Breaker,  say  20  tons^per  hour         .          .          .          .          .          .          .         '.          .11 

Elevator,      „  „  „  '•  .          .          .         ,          .          .          ....       9 

Coal  conveyor,    „     „      ..........   7 

Coke  conveyor  ',-...    .    .    .    .    .    .    .    .10 

65 

Thus  the  maximum  day  load  is  55  b.h.p.  and  the  minimum  night  load  28  b.h.p. 
Motors  of  this  type  should  run  at  an  average  efficiency  of  from  80  to  85  per  cent. 
Assuming  the  lower  figure,  so  as  to  allow  for  small  losses  between  generators  and 
motors,  the  following  current  would  have  to  be  supplied : — 

100 
55x^=69h.p. 

i.e.,  69  x  0-746  =  51-5  kilowatts. 

The  latter,  then,  must  be  the  power  of  the  dynamo,  i.e.,  it  must  generate  as 
a  maximum  234  amperes  at  a  pressure  of  220  volts.  In  practice  the  next  largest 
commercial  size  would  be  ordered,  say  55  or  56  kw. 

The  efficiency  of  a  dynamo  rarely  reaches  more  than  87  to  90  per  cent.,  there- 


230  MODERN   GASWORKS   PRACTICE 

fore  the  gas  engine  must  supply  sufficient  power  to  allow  for  this  loss.     The  power 
required  at  the  coupling  (assuming  a  dynamo  efficiency  of  88  per  cent)  is  : — 

56  X  100  =  63  6  kw ^  or  _ 

88 

But  1  h.p.  =  746  watts,  therefore  the  required  horse-power  of  the  gas  engine 
would  be — 

63,600 

=  85  b.h.p. 


746 

The  nearest  convenient  size  would,  therefore,  be  installed;  and  it  is  important 
to  note  on  what  basis  the  b.h.p.  of  the  engine  is  given  by  the  makers.  Frequently 
the  figures  given  in  catalogues  refer  to  the  maximum  power  obtainable  calculated 
on  a  town's  gas  having  a  calorific  power  of  so  much  as  700  B.Th.U.  Nominal  or 
indicated  horse-power  need  not  be  considered.  With  regard  to  duplication  of  the 
plant  it  must  be  remembered  that  although  the  day  load  amounts  to  55  h.p.,  at 
times  it  will  be  very  much  less  than  this  and  the  engine  will  not  have  a  high  load 
factor.  In  the  event  of  the  large  plant  being  used  for  night  work  the  load  factor 
would  be  lower  still  (at  times  only  about  20  per  cent.),  with  a  corresponding  increase 
in  gas  consumption.  During  the  night  there  may  be  an  average  required  horse- 
power of  20  at  the  gas  engine,  and  assuming  a  consumption  of  22  to  24  cubic  feet 
per  horse-power-hour  with  the  small  plant,  or,  alternatively,  34  to  38  cubic  feet 
per  horse-power-hour  with  the  large  set,  the  difference  between  the  consumption 
of  the  two  sets  is  13  cubic  feet  per  horse-power-hour.  It  will  be  understood  that 
this  excess  consumption  of  the  larger  engine  is  due  to  its  working  at  about  one- 
quarter  load  only.  By  using  the  larger  engine  on  the  night  load  (i.e.  for  about  10 
hours  at  a  stretch)  the  waste  of  gas  per  night  would  be : — 

10  x  13  x  20  =  2,600  cubic  feet ; 

and  if  valued  at  Is.  6d.  per  1,000  cubic  feet  the  monetary  loss  will  amount  to  about 
4s.  per  day,  or  £70  per  annum.  Thus  in  balancing  up  the  merits  of  a  single  installa- 
tion or  two  of  half  the  capacity,  it  will  be  borne  in  mind  that  a  saving  of  £70  per 
annum  would  be  equivalent  to  the  interest,  wear  and  tear,  and  depreciation  (in  all 
about  10  per  cent.)  on  a  capital  outlay  of  about  £700.  This  sum  would  more  than 
suffice  to  meet  the  extra  cost  of  plant,  switchboard,  etc.,  for  the  duplicate  plant. 
The  amount  of  current  necessary  for  electrically  driven  machines  (chargers  and 
dischargers)  may  be  taken  at  0-2  to  0-4  units  per  ton  of  coal  handled. 

THE  MOTOR 

The  motor  is  the  reverse  of  the  dynamo,  that  is  to  say  it  transforms  electrical 
into  mechanical  energy.  The  greater  portion  of  the  current  supplied  is  absorbed 
by  the  armature  windings,  whilst  a  small  portion  is  drawn  off  by  the  field  windings, 
and  the  mechanical  power  obtained  is  derived  from  the  energy  of  the  current  flowing 
through  the  armature  in  a  magnetic  field.  Compound- wound  motors  are  preferable 
for  general  use,  for  reasons  similar  to  those  which  apply  to  the  dynamo.  For  all 


ELECTRICAL   PLANT   IN   GASWORKS  231 

powers  they  maintain  approximately  equal  speeds,  which  is  not  the  case  with  the 
series  motor,  whose  speed  decreases  as  the  load  increases.  The  advantage  of  the 
latter  type,  however,  is  its  heavy  starting  torque,  which  makes  it  valuable  for  quickly 
operated  work  such  as  tramways,  cranes,  etc.  In  cases  where  sudden  release  from 
the  load  is  probable  the  series  motor  should  not  be  employed,  for,  owing  to  the  lack 
of  governing  power,  "  racing  "  would  result,  with  a  consequent  tendency  towards 
bursting.  The  compound- wound  motor,  whilst  combining  the  commendable  features 
of  the  shunt  and  series  type,  largely  eliminates  their  defects,  and  is  always  to  be 
recommended  for  general  gasworks  purposes.  In  order  to  effect  economy  in  replace- 
ments it  is  preferable  to  keep  to  one  type  of  motor  and,  if  possible,  to  one  make. 
It  is  not  advisable  to  put  down  a  larger  motor  than  recommended  by  the  makers, 
for  loss  in  efficiency  results  and  the  average  machine  from  a  recognized  maker  will 
stand  a  temporary  overload  without  ill  effect.  In  the  worst  atmospheres  and 
situations  totally  enclosed  motors  should  be  used.  These  have  to  be  of  somewhat 
larger  size  (and  are  consequently  more  expensive)  than  the  "  protected  "  types, 
in  order  to  avoid  the  temperature  rise  which  may  result  from  lack  of  ventilation. 
The  objection  to  the  enclosed  type,  namely,  difficulty  of  access,  has  recently  been 
overcome  by  providing  easily  removable  ends,  thus  exposing  for  observation  the 
essential  portions.  For  most  purposes,  however,  the  "  protected  "  type  is  sufficient. 
It  is  smaller  and  cheaper  than  the  enclosed  type,  and  is  fully  capable  of  meeting  all 
the  demands  made  upon  it  when  working  in  normal  conditions  of  atmosphere. 

SWITCHES   AND   ACCESSORIES 

The  switchboard  fulfils  a  function  of  extreme  importance,  consequently  every 
care  should  be  taken  to  ensure  that  each  detail  is  capable  of  the  work  demanded  of  it. 
The  switches  should  be  up  to  full  capacity,  and  the  workmanship  should  be  of  the 
best,  down  to  the  smallest  details  of  bars,  studs,  etc.  The  board  may  either  be  built 
into  the  wall  so  as  to  give  outside  access,  or  may  be  placed  well  away  from  it  so  as 
to  provide  ample  space  for  repairs.  The  fittings  on  the  board  will  vary  with  the 
requirements  and  with  different  arrangements  of  units  of  power ;  but,  generally 
speaking,  each  unit  of  plant  has  a  separate  panel,  and  the  feeding  units  require  a 
further  panel.  Each  panel  has  a  voltmeter,  ammeter,  main  switch,  and  field  regu- 
lating switch.  The  feeder  panel  will  have  main  switches  for  each  circuit  of  power 
equivalent  to  the  respective  motors.  Tell-tale  lamps  or  earth  detectors  should  be 
fixed.  These  consist  of  two  lamps  in  series ;  the  pole  at  which  earthing  occurs  is 
indicated  by  the  extinguishing  of  one  of  the  lamps.  There  is  usually  a  small  control 
board  in  the  retort  house  with  switches  operating  the  various  pieces  of  plant,  whilst 
the  motors  must  be  provided  with  starters — preferably  rheostats.  Each  should  be 
fitted  with  a  "  no- volt "  and  overload  release,  which  are  combined  safety  devices 
giving  full  protection  against  all  mishaps.  The  overload  release  cuts  off  the  current 
when  it  reaches  a  pre-arranged  amperage  should  there  be  an  unforeseen  stoppage 
or  "  jamming-up  "  of  the  coal  plant,  and  in  this  way  the  windings  of  the  motor  are 
prevented  from  being  burned  out.  Again,  the  starter  may  be  left  on  by  accident 
or  inattention,  and  when  the  current  is  off  the  "  no- volt  "  release  brings  it  back  to- 


232  MODERN  GASWORKS  PRACTICE 

'"  off,"  thus  preventing  burning  out  should  the  main  switch  be  turned  on  in  the 
absence  of  the  operator.  Ironclad  switches  should  be  made  use  of  on  the  retort- 
house  panel,  the  whole  being  boxed  in  and  fitted  with  a  glass  panel  for  observation 
purposes. 

With  regard  to  cabling,  electrical  reference  books  give  in  tabulated  form  the 
grades  and  gauges  of  cables  suitable  for  all  powers.  On  the  common  forms  of 
rating  it  is  as  well  to  work  to  that  which  gives  the  largest  cable,  as  this  item  is  a 
small  one  compared  with  the  total  outlay.  Armoured  cabling  is  preferable  for  most 
work,  owing  to  its  superior  resistance  to  wet  and  damp,  and  its  general  flexibility. 
All  cables  should  be  laid  in  stoneware  ducts ;  and  it  will  be  found  good  policy  to 
leave  a  spare  channel  or  two  for  use  in  case  of  possible  extensions  to  plant. 

CONSTRUCTIONAL  POINTS 

Many  gasworks  have  their  electrical  plant  installed  in  the  subway  on  the  charg- 
ing side  of  the  retort  house,  and  in  some  cases  in  a  partitioned  portion  of  the  coal 
store.  Although  economical,  this  is  not  a  desirable  practice  to  follow,  owing  to  lack  of 
space,  indifferent  ventilation,  and  the  dusty  atmosphere.  A  thin  brick  or  rein- 
forced concrete  building  entails  but  small  expense,  and  permits  of  the  house  being 
designed  to  suit  the  lay-out  of  the  plant,  and  not  the  reverse,  as  is  so  often  the  case. 
In  the  majority  of  existing  subways  it  is  impossible  to  put  down  a  direct-driven 
plant. 

All  trenches  for  cables,  gas  and  water  pipes,  etc.,  should  be  capable  of  easy 
inspection,  and  are  preferably  covered  with  some  form  of  grid.  If  this  is  not  done, 
a  small  inspection  chamber  should  be  built  in  at  every  point  at  which  the  direction 
of  the  cable  or  pipe  is  changed. 


CHAPTER   X 
GAS-MAKING  AND   OTHER   COALS 

THAT  coal  is  mineralized  vegetation  is  a  point  on  which  all  doubt  has  been  removed. 
It  is  best  denned  as  the  product  of  the  decay  of  vegetable  matter  under  the 
prolonged  influence  of  pressure,  heat,  and  moisture.  The  classification  of  coals  is 
based  upon  the  geological  period  of  their  formation,  the  two  main  groups  being 
known  as  "  carboniferous  "  and  "  tertiary."  It  is  the  former  which  are  generally 
distinguished  by  the  name  of  "  true  "  coals,  and  in  this  category  are  included  steam 
•coals  and  anthracites,  cannel  coals,  and  the  mis-named  bituminous  types  which, 
almost  solely,  are  suitable  for  gas-making  purposes.  The  tertiary  coals,  on  the 
-other  hand,  embrace  those  types  of  the  nature  of  lignite  or  brown  coal. 

Scientific  records  appertaining  to  the  gradual  formation  of  coal  from  vegetable 
matter  prove  of  little  interest  to  the  practical  gas-maker,  and  the  same  almost  may 
be  said  of  the  composition  of  coals  as  determined  by  ordinary  laboratory  methods. 
Nowadays,  the  gasworks  value  of  a  coal  is  gauged,  not  by  its  specific  gravity  or" 
its  unoxidized  hydrogen  content,  but  by  its  capability  to  conform  with  certain 
practical  expectations.  The  constitution,  as  distinct  from  the  composition,  of  coal 
is  still  more  or  less  shrouded  in  mystery,  although  recent  investigators,  such  as 
Wheeler  and  Lewes,  have  classified  the  main  components  in  a  manner  which  is  of 
distinct  service  to  those  directly  interested  in  carbonization.  Composition  as 
determined  by  ultimate  analysis  may  almost  be  said  to  be  of  academic  interest 
alone,  and — according  to  one  authority— is  "  as  likely  to  afford  an  idea  of  the  con- 
stitution of  coal  as  the  total  weights  of  stone,  metal,  glass,  and  other  materials 
forming  Cologne  Cathedral  would  convey  an  idea  of  its  architecture  and  design." 

The  methods  now  in  vogue  for  the  examination  of  coal  may  be  classified  into 
two  groups,  namely,  (a)  Destructive  methods,  and  (6)  Non- destructive  methods. 
Destructive  methods  have  proved  of  certain  usefulness  in  the  past,  but  it  is  now 
generally  realized  that  the  constitution  must  be  determined  by  such  means  as  will 
not  involve  any  radical  change  in  the  chemical  constitution  of  any  one  of  the  com- 
ponent parts  of  the  substance.  The  non- destructive  methods  which  comply  with 
this  condition  are,  notably,  microscopic  examination  of  sections  by  transmitted 
light,  the  use  of  special  solvents  such  as  pyridine,  aniline,  and  chloroform,  and 
contact  photography.  The  solvent  processes,  perhaps,  can  scarcely  claim  to  come 
within  the  sphere  of  non-destructive  methods,  but  their  application  has  proceeded 
along  with  the  scientific,  as  opposed  to  the  directly  chemical,  means,  and  has  resulted 
in  the  unearthing  of  much  of  the  valuable  information  now  at  our  disposal. 

233 


234 


MODERN   GASWORKS   PRACTICE 


THE   ORIGIN  OF   COAL 

It  is  not  proposed  to  follow  out  in  detail  the  gradual  formation  of  coal  from 
the  original  vegetable  matter.  Sufficient  is  it  to  say  that  the  respective  changes 
are  partly  physical  and  structural,  and  partly  chemical.  The  accompanying  dia- 
gram (Fig.  185)  enables  the  changes,  so  far  as  the  salient  properties  and  constituents- 

of  the  coal  are  concerned,  to  be 
followed  up.  From  this  it  will  be 
noticed  that  the  looseness  of 
structure  of  the  original  matter 
gradually  gives  way  to  a  more 
compact  and  homogeneous  mass, 
whilst  the  volatile  bodies  are 
progressively  displaced  by  con- 
stituents of  a  "  fixed  "  nature. 
The  moisture  (i.e.  the  hygroscopic- 
water),  hydrogen,  oxygen,  and 
nitrogen  of  the  cellulose  all  tend 
to  be  expelled,  whereas  the  car- 
bon remains,  and  increases  in 
proportion  as  the  process  ad- 
vances. The  carbon,  it  must  be 
understood,  increases,  not  syn- 
thetically, but  merely  owing  to 
the  evolution  of  the  remaining 
constituents ;  which  fact  is  best 
illustrated  by  recalling  that  the 
volume  of  the  final  substance 
amounts  to  only  one-tenth  to 
one- sixteenth  of  the  original  vege- 


Volatile  Matter 


Calorifc  Power 


Specific  Gravity 


Hydrogen 


Oxygen 


Nitrogen 


1-2  2  1-0 

(Very  Variable) 


FIG.  185. — THE  FORMATION  OF  COAL. 


(The  figures  for  the  various  properties  and  constituents  vary  con- 
siderably for  the  same  types  of  coal.  Those  given  above  represent 
the  average.) 


tation  from  which  it  was  formed. 
Cellulose,  one  of  the  main 

constituents  of  vegetable  tissues,, 
may  be  considered  as  the  basis  from  which  the  gradual  evolution  of  coal  can  be 
conveniently  followed.  In  its  purer  forms  cellulose  is  best  known  to  us  as  cotton- 
wool and  paper.  It  has  been  shown  that  the  carbonic  acid  exhaled  by  animal 
life  and  resulting  from  all  forms  of  combustion  is  regenerated  into  oxygen  by  plant, 
life  coupled  with  the  agency  of  the  sun.  Expressed  chemically  in  its  most  simple  form,, 
the  nature  of  this  extremely  involved  action  is  somewhat  as  follows : — 

6  C02  +  5H20  -  C6H1005  (cellulose)  +  602. 

Experimental  results  in  connexion  with  the  artificial  conversion  of  cellulose^ 
indicate  that  it  undergoes  changes  on  the  following  lines  : — 

4C6H1005  =  C21H1602  (coal-like  residue)  +  3C02  +  12H20. 


GAS-MAKING   AND   OTHER   COALS  235 

Although,  however,  this  may  be  true  for  artificial  conversion,  we  know  that 
in  all  natural  conversion  methane  is  produced ;  thns,  considering  pure  cellulose , 
humus  matter  would  be  given  by  the  decomposition,  and  the  reaction  would  approach 
the  following  : — 

6(C6H1005)  =  C21H2008  (humus)  +  SCO,  +  7CH4  +  6H20. 

Bergius  says  that  the  differentiation  of  the  various  types  of  coal  is  not  due  to 
the  time  occupied  in  their  formation,  or  to  the  prevailing  temperature,  but  to  marked 
increase  in  the  pressure ;  and  he  supports  his  theory,  and  shows  it  to  be  in  con- 
formity with  geological  facts,  by  pointing  out  that  anthracite  has  been  formed  where 
the  earth's  crust  has  become  folded,  thus  squeezing  the  layers  of  carbonaceous 
matter  to  a  terrific  extent.  Peat,  lignite,  bituminous  coals,  and  anthracite  form 
a  series  further  and  further  removed  from  vegetation  and  wood  in  composition  and 
character.  The  brown  colouring  of  the  lignite  is  a  transition  stage  to  the  black  of 
the  coal,  and  whilst  the  vegetable  structure  disappears  the  specific  gravity  increases 
uniformly,  until  (as  is  now  not  generally  disputed)  the  final  stage  of  conversion  is 
arrived  at  by  the  formation  of  graphite  containing  100  per  cent,  of  carbon.  A 
point  of  importance  to  note  is  that  a  portion  of  the  total  carbon  is  in  such  a  state 
of  combination  that  it  is  capable  of  being  volatilized,  but  this  proportion  decreases 
as  the  formation  proceeds.  It  is  for  this  reason  that  steam  coals  and  anthracites, 
are  of  no  use  to  the  gas  engineer,  owing  to  their  indifferent  capabilities  as  regards 
gas  yields  and  coke.  Steam  coals  are  intermediate  in  composition  between  bitumin- 
ous coals  and  anthracite,  and  should  not  be  confused  with  the  latter.  In  average 
bituminous  coals,  as  used  for  gas-making,  the  volatile  carbon  amounts  to  from  15 
to  20  per  cent,  of  the  total  carbon,  and  is  of  extreme  importance,  in  that  it  accounts  on 
distillation  for  the  most  valuable  constituents  of  the  gas  and  tar. 

THE   CONSTITUTION  OF   COAL 

As  previously  stated,  the  constitution  of  coal  is  not  as  yet  wholly  understood, 
and  new  light  is  continually  being  shed  on  the  final  mode  of  existence  of  the  degrada- 
tion products  of  the  original  vegetation.  Investigators  such  as  Lewes,  however, 
have  definitely  established  the  presence  of  four  fundamental  bases  in  the  substance, 
and  these  are  classified  as  follows  : — 

(a)  Carbon  residuum. 
(&)  Humus  bodies. 

(c)  Resin  bodies. 

(d)  Hydrocarbons. 

In  general,  the  various  types  of  coal  owe  their  varying  characteristics  to  the 
proportions  in  which  these  substances  are  present,  and  each  of  the  constituents 
has  its  own  distinguishable  products  of  decomposition  when  subjected  to  distillation. 
For  instance,  the  ability  to  form  coke  and  to  yield  a  high  proportion  of  gaseous 
products  depends  upon  whether  the  hydrocarbons  and  resin  bodies  are  in  excess 
(in  which  case  the  coal  is  of  the  gas-making  type),  or  whether  the  carbon  residuum 
or  humus  bodies  are  present  in  the  greater  proportion,  when  a  non-caking  coal  of 


236 


an  anthracite  nature  results.  In  fact,  as  the  anthracite  stage  is  approached  the 
constituents  are  composed  largely  of  the  carbon  residuum  basis,  the  remainder 
•consisting  chiefly  of  resin  compounds.  Lewes  says  that  for  a  coal  to  have  the  property 
of  caking  or  "  coking,"  the  resin  bodies  and  hydrocarbons  have  together  to  be  present 
in  the  proportion  of  at  least  50  per  cent.  In  the  ordinary  type  of  gas  coal  the  four 
•constituents  are  present  in  approximately  the  following  proportions  : — 


Carbon  residuum 
Humus  bodies 
Resin  bodies    . 
Hydrocarbons  . 


30  per  cent. 

20 

25 

25 


With  an  anthracite  coal,  on  the  other  hand,    the  distribution  would  be  more 
in  accordance  with  the  following : — 


Carbon  residuum 
Resin  bodies    . 


72  per  cent. 

28 


(b)  Non-Caking 


FIG.  186. — CHART  SHOWING  APPROXIMATE  CONSTITUTION  OF  THE  CONGLOMERATE  OF  VARIOUS  TYPES 

OF  COAL. 


In  this  case  it  will  be  seen  that  the  high  calorific  power  of  the  anthracite  coals 
is  chiefly  dependent  upon  the  entire  elimination  of  the  low  heating-power  constituents. 
For  instance,  the  humus  bodies  (which,  on  heating,  account  largely  for  water  vapour, 
carbonic  acid,  and  carbonic  oxide,  having  a  comparatively  low  calorific  power)  give 
way  to  resins  and  carbon.  It  is  the  humus  which  accounts  largely  for  the  low  heating 


GAS-MAKING   AND   OTHER   COALS 


237 


value  of  the  lignites.  The  approximate  calorific  powers  of  the  four  fundamental 
substances  may  be  taken  as  follows : — 

Resin  bodies    .  . 16,400  B.Th.U.  per  Ib. 

Hydrocarbons  .  .  ...                              .  15,900 

Carbon  residuum  .  ......  14,600           „         „ 

Humus  bodies  .  ......  13,300           „         „ 

From  the  above  it  will  be  seen  that  the  maximum  calorific  power  is  yielded 
when  the  presence  of  the  humus  bodies  can  no  longer  be  traced,  as  is  the  case  with 
the  anthracites  and  many  of  the  steam  coals. 

Lewes  points  out  that  the  composition  of  the  humus  and  resin  bodies  is  a 
follows  :— 

Carbon.  Oxygen.       Hydrogen. 

Humus        .........     63  32  5 

Resins         ......  .79  11  10 

He  shows  that  the  whole  of  the  oxygen  present  in  the  coal  is  due  to  these  two 
bases.  Hydrogen,  in  addition,  is  present  in  the  hydrocarbon  substance,  but  the 
unsaturated  hydrocarbons  in  the  gas  are  chiefly  derived  from  the  resinic  compounds, 
whilst  the  hydrocarbon  base  is  responsible  for  the  paraffin  group.  In  the  past,, 
authorities  on  carbonization  have  emphasized  the  importance  of  the  "  unoxidized 
hydrogen  "  content  of  the  coal,  and  by  deducting  the  quantity  of  combined  hydrogen 
from  the  total  have  arrived  at  a  figure  for  hydrogen  which  they  consider  of  importance 
owing  to  the  supposition  that  this  is  the  only  available  hydrogen  for  the  yield  of 
free  hydrogen  and  hydrocarbons  in  the  gas.  Thus  a  coal  which  on  ultimate  analysis 
shows  5  per  cent,  of  hydrogen  and  8-8  per  cent,  of  oxygen  would  be  rated  on  an  "  un- 

/         8-8\ 
oxidized  hydrogen  "  content  of   (  5  -      -  J,  =3-9  per  cent.  It  must  be  pointed  out, 

however,  that  only  a  portion  of  the  original  oxygen  in  the  coal  combines  to  form  water 
in  this  manner,  a  further  material  amount  being  found  in  combination  in  the  con- 
densible  vapours  forming  the  tar,  and  as  oxides  of  carbon.  Primarily,  the  proportion 
of  oxygen  gives  a  useful  indication  of  the  extent  to  which  humus  bodies  are  present 
in  the  coal,  whilst  the  direct  subtraction  of  the  hydrogen  percentage  from  the  oxygen 
percentage  enables  an  opinion  to  be  formed  as  to  calorific  power.  For  instance, 
Constam  and  Kolbe  have  given  the  following  figures  : — 


Coal. 

Oxygen. 

Hydrogen. 

Difference. 

Net 
calorific  power. 

Nottingham,  bright     . 

per  cent. 

10-20 

per  cent. 

5-30 

4-90 

B.Th.U.  per  Ib. 
13,912 

Ditto        hard     .... 

9-24 

4-97 

4-27 

14,072 

Durham  I          

5-66 

5-48 

0-18 

15,392 

Durham  II        ..... 

3-70 

5-46 

1-76 

15,766 

These  figures  clearly  indicate  that  with  coals  of  the  bituminous  type  the  calorific 
power  is  inversely  proportional  to  the  excess  of  oxygen  over  the  hydrogen,  and  there- 
fore bears  a  ratio  to  the  quantity  of  humus  bodies  present.  At  the  same  time  a  know- 


238    .   • 

ledge  of  the  percentage  of  oxygen  is  of  decided  value  to  the  gas  engineer,  in  that  it 
conveys  a  useful  idea  as  to  the  proportion  of  volatile  matter.  The  latter  is  accounted 
for  by  both  humus  and  resin  constituents  (in  addition  to  the  hydrocarbon  bases),  in 
both  of  which  oxygen  is  present.  Lewes  has  emphasized  the  importance  of  oxygen 
and  has  laid  down  the  following  axioms  : — 

(1)  The  higher  the  oxygen  in  the  coal,  the  higher  the  volatile  matter. 

(2)  The  higher  the  oxygen,  the  lower  the  coke  yield. 

(3)  The  higher  the  oxygen  the  greater  the  amount  of  CO  and  C02. 

(4)  Oxygen  above  10  per  cent,  or  below  4  per  cent,  means  inferior  coke  or 
indicates  a  non-coking  coal. 

As  an  illustration  of  the  last  statement  the  figures  for  the  types  of  non-caking 
•coals  (about  13  per  cent,  of  oxygen)  and  for  anthracites  (0-25  per  cent.)  may  be 
recalled. 

It  must  be  realized  that  each  of  the  fundamental  constituents  accounts  for  its 
own  particular  series  of  decomposition  products.  These,  moreover,  not  only  undergo 
variation  according  to  the  temperature  of  distillation  employed,  but  are  further 
affected  by  secondary  reactions  resulting  from  the  influence  of  the  heated  walls  of 
the  vessel  in  which  the  coal  is  treated. 

GAS-MAKING  COALS 

The  quantity  of  coal  now  used  for  gas-making  purposes  in  the  United  Kingdom 
amounts  to  about  16,000,000  tons  per  annum.     Generally  speaking,  it  may  be  said 
that  the  favourite  coals  of  the  gas  engineer  are  those  occurring  in  the  Northumberland 
and  Durham  districts.     Other  fields  from  which  large  supplies  are  drawn  are  those 
of  West  Yorkshire,  South  Lancashire,  Nottingham,  and  Derbyshire,  also  Stafford- 
shire and  Warwickshire.     Owing  to  the  decided  variation  in  quality  which  occurs 
in  coals  mined  in  adjacent  or  even  in  the  same  seams  it  is  difficult  to  distinguish  with 
accuracy  between  the  products  of  the  different  districts ;  in  fact,  it  is  by  no  means 
uncommon  to  find  both  steam  coal  and  gas-making  types  occurring  in  the  seams  of 
any  one  mine.     The  problem  with  which  the  gas  engineer  is  chiefly  confronted  is  that 
of  balancing  gas-making  capabilities  against  expense  of  delivery.     In  the  majority 
of  cases  it  will  be  found  most  economical  to  take  the  coal  nearest  to  the  point  of 
•consumption,  even  though  the  quality  is  not  all  that  might  be  desired. 

In  general,  the  typical  analysis  of  a  gasworks  coal  of  good  quality  will  approxi- 
mate to  the  following,  although  as  regards  ash  content  it  is  by  no  means  an  uncommon 
occurrence  to  find  the  inert  matter  even  in  coals  of  good  reputation  mounting  up  to 
as  much  as  10  per  cent. 

TYPICAL  GAS-MAKING  COAL 

Carbon    .          .          .        , .  •   .          .         ,          ,      <    .          .          .80     per  cent. 

Hydrogen         ....          .          .          .          .         .         .          .          .     5-5 

Oxygen  .          .          ...       '  .          .          .         .          .         .'        .          .8-8 

Nitrogen  ..      _...•....»         ,    -     .          .          .          .  .        .          .     1-5 

Sulphur  .          .          ......          .          .          .          .         .          .          .0-8 

Ash     .....    -.          .          .          .          .          .          .          .3-4 

Volatile  matter         .'..;..>        .         -.  30  to  35 

Calorific  power         .         .  -       .          .          .      -   .          .          .      14,400  B.Th.U.  per  Ib. 


GAS-MAKING   AND   OTHER   COALS 


239 


In  the  following  table  there  are  set  forth  the  differences  in  ultimate  analysis  of 
typical  coals  from  the  various  seams  of  the  country  ;  but,  as  already  pointed  out, 
it  must  be  recognized  that  this  standard  of  judgment  is  not  to  be  relied  upon.  If 
used  intelligently,  however,  the  chemical  composition  of  a  coal  will  give  some  insight 
into  its  value  for  gas-making  purposes.  Particular  attention  should  be  given  to  the 
proportions  of  ash,  oxygen,  and  sulphur.  With  regard  to  the  last-named,  although 
a  certain  amount  may  be  chemically  combined  with  the  chief  elements,  and  may 
accordingly  form  some  portion  of  the  conglomerate,  the  quantity  so  combined  is 
extremely  small,  and  forms  but  a  fraction  of  that  existing  as  iron  pyrites  ("  brasses  ") 
or  sulphates. 

TYPICAL  BRITISH  COALS 


Carbon. 

Hydrogen. 

Oxygen. 

Nitrogen. 

Sulphur. 

Ash. 

Durham    

81-1 

5-37 

7-01 

1-56 

1-12 

3-84 

Lancashire      .... 

77-91 

5-40 

9-32 

1-31 

1-45 

4-61 

Nottingham   .... 

77-36 

5-66 

10-22 

1-34 

1-65 

3-77 

Derbyshire      .... 

79-68 

4-94 

10-28 

1-41 

1-01 

2-68 

Scotland   

78-53 

5-63 

9-22 

1-00 

1-11 

4-51 

So  far  as  the  Durham  types  are  concerned,  New  Pelton  and  Holmside  qualities 
are  classified  as  "  gas  bests,"  whilst  "  gas  specials  "  include  Thornley,  Wearmouth, 
and  Londonderry.  "  Gas  seconds  "  comprise  types  such  as  Pelton  Main.  Of  the 
Derbyshire  varieties  the  "  deep  softs  "  are  those  chiefly  employed  for  gas  production, 
the  best-known  qualities  being  Birley  Silkstone  and  Mickley  Thin.  The  West  York- 
shire fields  provide  the  chief  sources  of  supply  for  the  many  large  gasworks  of  that 
county,  and  of  the  typical  gas  coals  the  most  notable  seams  are  the  celebrated  Silk- 
stone,  also  the  Stanley  Main,  Beeston,  and  Middleton  varieties.  In  addition,  cannel 
seams  are  still  being  worked,  but  only  to  a  comparatively  small  extent. 

CANNEL   COAL 

Cannel  or  "  candle  "  coal  is  unsuited  to  the  present-day  requirements  of  gas- 
works. It  was  somewhat  extensively  used  in  the  days  when  statutory  requirements 
as  to  illuminating  power  were  more  severe,  and  before  the  general  introduction  of 
carburetted  water-gas  as  a  source  of  enrichment.  Although  varying  in  constitution 
to  some  considerable  extent,  it  is  an  extremely  rich  coal  containing  a  high  proportion 
of  resinic  bases.  As  regards  its  occurrence,  the  seams  in  some  cases  turn  gradually, 
almost  imperceptibly,  into  a  bastard  cannel,  and  finally  merge  into  shale.  Its 
characteristics  resemble  in  many  ways  those  of  the  Scottish  gas-making  coals.  Cannel 
may  be  said  to  range  in  position  between  lignites  and  bituminous  coals,  and  contains 
on  an  average  as  much  as  45  per  cent,  of  volatile  matter.  The  chief  objection  to  the 
use  of  cannel  is  the  poor  quality  coke  which  it  yields.  The  coke,  owing  to  its  powdery 
nature  and  high  percentage  of  inert  matter,  is  practically  useless  for  fuel  purposes. 
In  some  cases  cannel  coke  will  contain  upwards  of  60  per  cent,  of  ash.  The  specific 


240 


MODERN   GASWORKS   PRACTICE 


gravity  of  cannel  is  rather  higher  than  that  of  bituminous  coal,  and  lies  in  the  neigh- 
bourhood of  1-27.     The  ultimate  analysis  varies  between  the  following  limits  : — 


Hydrogen       .          .          .          .          ...                  '. 

5    , 

10 

Oxygen 

.    4-5    , 

15 

Nitrogen         .          .          .          .                   .         .         . 

1    , 

2-5 

Sulphur           .          .          .          .          .                   .          . 

.    0-3    , 

2-5 

Ash 

5    . 

20 

As  regards  gas-making  yields  a  high  quality  cannel  is  capable  of  giving,  in  excep- 
tional oases,  14,000  cubic  feet  of  gas,  with  an  illuminating  power  of  from  35  to  45 
candles.  The  price  of  the  coal,  however,  is  prohibitive  ;  and  in  normal  times 
ranges  around  35s.  per  ton  (delivered  London)  for  types  such  as  the  well-known  Bog- 
head, whilst  the  Yorkshire  variety  is  valued  at  28s.,  with  the  poor  quality  Derbyshire 
type  at  18s.  Cannel  tar  is  of  a  distinctly  paraffinoid  nature. 


SPACE   OCCUPIED   BY   COALS,   ETC. 

For  the  purpose  of  estimating  stocks  of  coal  or  coke  it  is  necessary  to  have  some 
idea  of  the  space  occupied  per  unit  of  weight  by  various  solid  substances.  For  the 
use  of  the  gas  engineer  the  following  figures  will  be  found  suitable,  but  the  physical 
condition  of  the  material  may  account  for  some  variation  in  either  direction  :— 

1  Ton  of— 

Ordinary  gas  coal  (unbroken)  occupies  .          .          .          .          .     42  to  43  cubic  feet. 

„  „         (broken)  ......  40 

Cannel  coal  (varies  considerably) 

Anthracite 

Coke  (unbroken) 

Breeze 

Lime  (1  yard  =  12J  cwts.) 

Oxide  of  iron  (Dutch) 

„         „       (Prepared) 

„         „       (Belgian) 
Sulphate  of  ammonia 

CONSIDERATIONS   AFFECTING   THE   PURCHASE   OF   COAL 

It  is  extremely  difficult  to  lay  down  any  hard  and  fast  stipulations  on  which  to 
base  the  purchase  of  coal  intended  for  gas-making  purposes.  A  final  choice  should 
not  necessarily  be  influenced  by  a  comparison  of  "  makes  "  per  ton  and  total  residuals, 
but  by  a  consideration  of  net  financial  standing  after  all  charges  have  been  balanced 
against  receipts.  It  is  for  this  reason  that  many  concerns  still  adhere  to  the  poorer 
classes  of  coal  where  the  collieries  producing  these  are  near  the  gasworks,  thus  saving 
in  freightage  charges.  High  yields  of  gas  per  ton  are  undoubtedly  alluring,  but 
useful  contrasts  between  the  working  results  of  different  gasworks  cannot  be  drawn 
on  this  basis.  The  only  true  gauge  is  the  annual  or  half-yearly  balance-sheet. 

Most  of  the  coals  used  in  the  gasworks  of  this  country  are  of  necessity  rail- 
borne,  and  the  following  table  gives  the  charges  per  ton  from  the  chief  colliery  centres. 


OU  LU  "±i» 

35  „  39 

* 

85  „  92 

60  „  65 

42 

45 

41 

40 

47  to  48 

GAS-MAKING   AND   OTHER   COALS  241 

to  London.     It  is  not  possible  to  lay  down  any  rate  based  on  number  of  miles  dividing 
works  from  colliery. 

AVERAGE  RAILWAY  CHARGES  FROM  CHIEF  COLLIERY  GROUPS  TO  LONDON 

Warwickshire  (the  nearest  field  to  London  with  the  exception  of 

Kent) 5*.  Id.  to  5s.  Id. 

Leicestershire  .          .          .          .          .          .          .          .          .          .  5s.  Id.  „    5s.  lid. 

Nottingham 6s.          „     6s.  6d. 

South  Derbyshire 6s.          „     6s.  2d. 

North  Derbyshire     . 6s.  2d.    „     6s.  8d. 

Catinock  Chase  District    ........  5s.  lOd. 

North  Staffordshire 6s.  8d. 

South  Yorkshire       . 7s.  2d. 

Lancashire       .          .          .          .-         .          .'         .          .          .          .  Is.  8d.  to  Is.  lOd. 

South  Wales .  ,  7*.  2d.    „   Is.  9d. 

These  rates  are  to  the  main  London  stations,  and  in  every  case  Is.  per  ton  extra 
is  charged  for  wagon  hire  unless  the  consignee  provides  his  own.  South  of  the 
Thames  or  exceeding  150  miles  from  the  colliery  the  rate  is  increased  to  Is.  3d.  The 
average  cost  of  ship-borne  coal  in  normal  times  (delivered  alongside  London  from, 
say,  Newcastle)  is  in  the  neighbourhood  of  3s.  per  ton,  if  fair-sized  colliers  can  be 
taken  up  to  the  point  of  delivery.  If  transference  into  barge  is  necessary,  the  cost 
will  be  increased  to  about  3s.  9rf.  per  ton. 

Coal  for  all  the  larger  gasworks  is  purchased  by  contract,  usually  for  a  period 
of  twelve  months.  In  the  ordinary  way  these  contracts  are  entered  into  as  dating 
from  1st  July  in  each  year,  for  a  specified  monthly  quantity.  In  the  majority  of 
cases  a  fixed  yearly  price  is  settled,  but  occasionally  a  somewhat  higher  price  for  the 
six  winter  months  has  to  be  conceded.  This  margin  may  amount  to  6d.  or  Is.  per 
ton.  The  various  coal  groups  have  by  this  time  established  a  reputation,  either 
good  or  indifferent,  for  the  class  of  material  they  turn  out ;  and  as  each  district  or 
series  of  seams  has  its  own  particular  name,  the  name  alone  is  often  sufficient  to  con- 
vince the  purchaser  of  what  he  is  buying.  For  all  that,  coals  occurring  in  the  same 
locality  vary  considerably,  and  too  much  reliance  must  not  be  placed  in  a  name. 
There  are  many  methods  of  arriving  at  an  approximate  comparison  between  the 
suitability  of  different  coals  for  gas-making  purposes,  the  chief  being  the  following  : — 

(a)  Proximate  analysis.  That  is  to  determine,  chiefly,  the  volatile  content. 
This  gives  some  gauge  of  the  gas-yielding  and  coking  properties  of  the  coal.  The 
test  is  best  carried  out  by  Dr.  Lessing's  method,  in  which  electrical  heating  is 
employed. 

(6)  The  calculation  of  pounds  of  sperm  per  ton,  or  the  pounds  of  sperm  which 
can  be  purchased  for  a  shilling.  This  is  a  time-honoured  method  which  has  proved 
of  some  value  in  the  past,  but  which  is  scarcely  in  conformity  with  modern  applica- 
tions of  gas.  To  obtain  the  value  of  a  coal  in  pounds  of  sperm  per  ton  the  make  of 
gas  per  ton  is  divided  by  5  (which  is.  the  cubic  feet  of  gas  consumed  by  the  standard 
test  burner  per  hour)  ;  the  result  is  then  multiplied  by  the  illuminating  power  and 
by  120  (120  being  the  number  of  grains  consumed  per  hour  by  the  standard  sperm 

R 


242  MODERN   GASWORKS   PRACTICE 

candle).    Finally,  it  is  necessary  to  divide  by  7,000,  which  is  the  number  of  grains 
in  1  Ib.    Put  briefly  :— 

Pounds  of  sperm  per  ton  =  make  X  illuminating  power  x  -003428. 

(c)  Calculation  at  current   prices   of   total  yields  of  gas,  coke,  etc.,  obtained 
from  a  ton  of  the  coal.     The  figure  obtained  is  then  balanced  against  the  cost  of  the 
coal,  and  comparison  between  various  coals  is  made  on  these  lines.     This  method 
cannot  be  applied  with  accuracy,  and  is  not  to  be  recommended. 

(d)  The  use  of  a  coal- testing  plant.     On  the  larger  works  it  is  still  customary 
to  submit  small  samples  taken  from  fresh  consignments  of  coal  to  a  laboratory'experi- 
mental  plant.     The  total  gas  evolved,  in  addition  to  the  main  by-products,  is  then 
carefully  collected  and  measured.     The  usual  procedure  is  to  take  y-Q1^  ^th  part  of  a 
ton  of  coal  (2-24  Ib.),  which  is  carbonized  in   a  small  cast-iron  a-shaped  retort, 
5  inches  x  4  inches  x  3  feet  in  length. 

The  coal-testing  plant  of  the  Birmingham  Corporation  gasworks  is  probably 
the  most  elaborately  equipped  of  those  now  in  use.  It  is  on  an  exceedingly  large 
scale,  and  in  reality  forms  a  complete  gasworks  in  itself.  Various  types  of  retort 
settings  are  in  use,  including  regenerative  horizontal  beds,  and  both  intermittent 
and  continuous  vertical  systems.  The  horizontal  test  bench  is  capable  of  dealing 
with  31  tons  of  coal  per  diem,  and  consists  of  four  beds  of  full-sized  through  retorts. 
The  intermittent  vertical  installation  has  a  capacity  of  14  tons  a  day,  and  the  con- 
tinuous bench  is  capable  of  dealing  with  20  tons  per  diem.  Elaborate  apparatus 
is  installed  for  the  purpose  of  arriving  at  an  accurate  knowledge  of  the  capabilities 
of  the  various  coals  tested,  and  their  behaviour  under  different  systems  of 
carbonization. 

(e)  Comparison  by  "  gas  multiple."     This  is  one  of  the  most  recent  methods, 
and  can  be  looked  upon  as  affording  the  most  satisfactory  means  of  comparing  the 
gas-yielding  proclivities  of  various  coals.     The  yield  per  ton  is  obtained  by  careful 
experiments  in  the  test  plant,  and  the  illuminating  power  of  the  gas  evolved  is  noted. 
The  "  make  "  of  gas  is  then  multiplied  by  the  candle  power,  and  the  result  gives  the 
"  gas  multiple." 

For  example,  two  coals  (a)  and  (6)  might  be  tested  with  the  following  results  :— 

(a)  12,000  cubic  feet  of  gas  per  ton.     Candle  power,  15. 

(6)  13,000          „  „    ,        „  „  „     14. 

Then  for  (a)  the  gas  multiple  is  180,000,  and  for  (6)  it  is  162,000.  Coal  (a)  would 
then  be  adjudged  the  most  desirable  from  the  point  of  view  of  gas  yield.  In  some 
cases  it  is  customary  to  multiply  the  gas  "  make  "  by  the  calorific  power  of  the  gas, 
in  lieu  of  the  candle  power. 

Whatever  method  of  testing  is  undertaken,  the  importance  of  the  by-products, 
tar  and  liquor,  must  not  be  overlooked,  for  an  enhanced  yield  of  these  is  frequently 
more  profitable  than  a  slightly  increased  gas  "  make  "  obtained  from  some  other 
coal  or  by  varying  the  method  of  carbonizing  the  same  coal.  At  the  same  time  it 
must  be  borne  in  mind  that  a  low  gas  yield  means  more  coal  to  make  the  necessary 
quantity  of  gas,  consequently  higher  charges  for  handling  and  transport. 


GAS-MAKING   AND   OTHER   COALS  243 

CALORIFIC   POWER   RECOVERED 

Suggestions  have  recently  been  made  that  calorific  power  should  be  made  a 
basis  on  which  to  adjust  the  value  of  coal.  Thus  a  certain  price  per  ton  would  be 
charged  for  a  definite  calorific  power,  and  a  pro  rata  reduction  made  when  the  heating 
value  was  below  the  standard.  For  those  who  employ  coal  as  a  fuel  the  system  has 
many  advantages.  The  gas  engineer,  however,  is  concerned  not  so  much  with  the 
number  of  heat  units  in  his  original  coal,  but  with  the  number  which  will  be  recover- 
able on  distillation,  and — more  particularly — in  what  form  they  will  be  recovered.  The 
latter  consideration  is  rarely  accorded  the  share  of  attention  it  merits,  but  a  simple 
illustration  is  sufficient  to  indicate  its  importance.  Of  the  original  heat  units  in  a 
ton  of  coal  about  95  per  cent,  are  recovered  in  useful  form  in  (a)  the  gas,  (6)  the  coke, 
(c)  the  tar.  First,  it  must  be  considered  in  which  of  these  three  forms  the  B.Th.U. 
are  the  most  profitable.  Now,  10,000  B.Th.U.  are  contained  in  18  cubic  feet  of  gas, 
and  in  this  form  yield  approximately  frf.  On  the  other  hand,  10,000  B.Th.U.  are 
contained  in  about  y^th  Ib.  of  coke,  and  in  this  form  yield  ^d.  It  is  clear,  then, 
that  in  the  form  of  gas  the  recovered  heat  units  are  several  times  more  valuable  than 
is  the  case  when  they  are  recovered  in  the  coke,  even  when  the  cost  of  gas  into  holder 
is  considered.  The  original  calorific  .power  of  the  coal  should,  therefore,  be  realized 
in  the  gas  as  far  as  possible,  this  being  the  most  profitable  outlet  for  the  heat  units. 
According  to  investigation,  coke  accounts  for  about  60  to  65  per  cent,  of  the  original 
calorific  power  of  the  coal,  tar  for  from  6  to  8  per  cent.,  and  the  gas  for  25  to  35  per 
cent.,  whilst  a  loss  approaching  5  per  cent,  is  generally  found.  The  loss  will  be 
partly  accounted  for  by  retort  carbon,  and  may  be  partly  the  outcome  of  the 
.supposed  thermal  nature  of  the  carbonization  of  coal  (see  page  95). 

COAL   WASHING 

All  coals  as  won  from  the  pit  contain  varying  proportions  of  inert  matter  or 
otherwise  undesirable  impurities.  Chief  amongst  these  are  siliceous  and  calcareous 
matter,  also  shale  and  pyrites.  In  former  times  a  considerable  quantity  of  the  coal 
hewn  was  regarded  as  worthless  and  often  left  below  ground,  and  were  it  not  for  the 
methods  of  washing  employed  many  of  the  inferior  seams  would  be  unprofitable  to 
work.  With  the  perfecting  of  washing  apparatus  even  abandoned  measures  have 
been  reopened,  and  material  containing  so  much  as  20  per  cent,  of  impurities  is  ren- 
dered of  marketable  value.  In  such  cases  it  is  difficult  to  reduce  the  undesirable 
matter  below  about  6  per  cent.,  but  the  more  general  practice  is  to  treat  those  coals 
containing  originally  about  8  per  cent,  of  impurities,  these  being  ultimately  reduced 
to  2  per  cent,  or  even  under.  The  principle  of  coal  washing  is  based  upon  the  differ- 
ence in  the  specific  gravity  of  coal  and  of  the  impurities  intermixed  with  it.  Water  is 
the  separating  agent  employed,  and  if  the  mixture  is  allowed  to  fall  through  a  tank 
the  heavier  particles  will  sink  more  quickly  than  the  lighter  ones.  The  relative 
specific  gravities  of  the  various  substances  are  approximately  as  follows  : — 

Coal,  1-25. 

Shale,  2-5. 

Pyrites,  3-5  to  5. 


244  MODERN   GASWORKS   PRACTICE 

Coal  washers  now  in  use  consist  of  two  distinct  types,  namely : — 

(a)  Running  water,  down  some  form  of  inclined  trough. 

(6)  Mechanically  agitated  water. 

The  first  type  was  introduced  in  the  early  days  of  the  process,  and  is  fast  giving 
way  to  the  more  scientific  mechanical  plants.  Of  the  latter  plants  there  are  several 
varieties,  such  as  the  Blackett,  the  Elliott,  the  Robinson,  and  the  Baum  washers. 
In  nearly  all  types  it  is  customary  to  screen  the  coal  before  washing,  and  then  to 
treat  each  grade  as  desired  for  the  elimination  of  impurities.  The  Baum  washer, 
however,  is  operated  on  the  principle  of  "  first  wash,  then  classify,"  and  is  shown 
in  Fig.  187.  Any  coal  below  3|-inch  mesh  is  washed  without  previous  screening  in 
one  washer  box,  the  specifically  heavier  products  going  to  the  bottom  and  the 
lighter  products  (i.e.  the  coal)  going  away  with  the  water.  The  Baum  washer  is 
capable  of  dealing  with  any  quantity  of  coal  up  to  150  tons  per  hour,  and  the  applica- 
tion of  the  water  is  effected  by  air  at  a  pressure  of  about  2  Ib.  per  square  inch.  The 
air  valve  is  provided  with  a  sleeve  piston  which  is  raised  and  lowered  by  an  eccentric. 
When  the  valve  is  in  the  lower  position  air  passes  direct  from  the  blower  and  exerts 
its  full  pressure  on  the  surface  of  the  water.  When  the  valve  is  in  the  upper  position 
the  air  supply  is  cut  off  from  the  washer  box,  which  is  simultaneously  opened  to  the 
atmosphere.  In  this  way,  alternate  depression  and  rebound  of  the  water  take  place. 
The  coal  to  be  washed,  lying  on  the  grid  R,  is  thus  subjected  to  the  pulsations  of  the 
water,  and  the  dirt  falls  to  the  bottom,  whence  it  is  removed  by  the  elevator,  Q.  The 
worm  conveyor,  S,  collects  towards  the  elevator  any  dirt  deposited  further  along  the 
washer  box.  The  coal,  along  with  the  middles  and  light  dirt,  overflows  into  a  second 
section  of  the  washer  box,  where  it  undergoes  further  treatment,  the  good  products 
overflowing  at  N  to  be  dealt  with  according  to  requirements.  The  washing  water 
enters  at  T,  and  passes  with  the  washed  coal  over  the  outlet  N.  It  is  afterwards 
clarified  before  being  returned  to  the  box. 

Coal  after  washing  is  usually  allowed  to  drain  in  bunkers  and  to  dry  in  the  air. 
The  cost  of  washing  by  modern  methods  is  trivial,  amounting  to  from  Id.  to  4d.  per 
ton,  according  to  the  capacity  of  the  plant,  whilst  the  value  of  the  coal  may  be  en- 
hanced by  the  process  by  anything  from  Qd.  to  Is.  per  ton.  As  regards  the  percent- 
age of  moisture  in  washed  coal,  this  depends  upon  the  size  of  the  coal,  weather  con- 
ditions, etc.,  but  it  may  be  as  much  as  10  per  cent,  over  that  in  the  normal  sample. 

THE  STORAGE,  SPONTANEOUS  COMBUSTION,  AND  DETERIORATION 

OF   COAL.1 

The  problem  of  the  spontaneous  combustion  of  coal  is  one  which  the  gas  engineer 
is  continually  called  upon  to  face,  owing  to  the  fact  that  the  bituminous  coals  used 
on  gasworks  suffer  most  in  this  respect.  Cannel  coals  are  less  affected,  and  steam 
coals  and  anthracite  are  least  liable  of  any.  Originally,  there  was  a  general  opinion 
among  gas  engineers  that  spontaneous  ignition  was  due  to  the  oxidation  of  the 
"  brasses  "  or  pyrites  in  the  coal,  and  that  the  action  was  greatly  accelerated  by 
damp  and  moisture,  the  pyrites  being  oxidized  by  the  oxygen  contained  in  the  water. 
1  See  the  author's  article  in  the  Journal  of  Gas  Lighting,  vol.  cxix.  page  616. 


Fm.  187.— THE  BAUM     COAL  WASHES. 
245 


246  MODERN   GASWORKS   PRACTICE 

This  idea  probably  originated  in  the  fact  that  if  a  quantity  of  pyrites  is  picked  from 
the  coal,  made  into  a  heap,  and  then  exposed  to  air  and  moisture,  the  heat  of  the 
pile  rapidly  rises,  owing  to  the  oxidization  of  the  sulphur  due  to  the  action  of  the  air 
and  moisture.  In  many  cases  a  temperature  will  be  reached  at  which  combustion 
in  air  begins,  and  the  mass  will  then  burst  into  flame.  In  contradiction  of  this  theory, 
however,  it  must  be  pointed  out  that  while  some  coals  containing  a  very  high 
percentage  of  pyrites  are  quite  safe,  those  containing  a  small  proportion  often  give 
great  trouble  when  stacked. 

There  seems  to  be  little  doubt,  then,  that  spontaneous  combustion  is  the  outcome 
of  a  combination  of  several  causes,  and  that  while  pyrites  itself  is  not  alone  respon- 
sible, it  plays  some  subsidiary  part  in  assisting  the  action.  Factors  such  as  the  size, 
dampness,  proportion  of  volatile  matter,  and  general  composition,  all  play  their  part 
in  bringing  about  a  rise  in  temperature.  It  is,  however,  interesting  to  note  that 
conclusions  arrived  at  by  the  United  States  Bureau  of  Mines  w^ere  that  moisture  plays 
no  part  in  promoting  spontaneous  heating,  and  that  high  volatile  matter  does  not  of 
itself  increase  the  liability  to  fire. 

It  is  common  knowledge  that  coal  as  soon  as  it  leaves,  the  seam  has  a  great 
avidity  for  oxygen,  and,  remarkable  as  it  may  seem,  the  greater  the  proportion  of 
oxygen  in  combination  with  the  coal  the  greater  appears  to  be  its  proclivities  for 
absorbing  an  additional  quantity  from  the  air.  Lewes  pointed  out  that  the  "  resin 
bodies  are  the  compounds  present  in  the  coal  most  likely  to  possess  this  property. 
It  is  the  chemical  actions  so  caused  which  lead  to  slow  combustion,  and,  when 
accelerated  by  any  rise  in  the  surrounding  temperature,  this  is  capable  of  generat- 
ing sufficient  heat  to  lead  to  the  spontaneous  ignition  of  masses  of  broken  coal  large 
enough  to  prevent  the  escape  of  heat  as  it  is  developed."  Many  bituminous  coals 
will  absorb  more  than  three  times  their  volume  of  oxygen  ;  but  after  a  time  they 
get  coated  with  an  oxidized  surface,  and  their  absorptive  properties  become  less, 
vigorous  until  new  surfaces  are  exposed  by  the  breakage  of  lumps,  etc.  It  is  prob- 
able, then,  that  the  spontaneous  heating  in  coal  heaps  is  due  to  the  rise  of  tempera- 
ture occasioned  by  the  oxidation  of  part  of  the  carbon  together  with  the  sulphur  in 
the  coal ;  and  in  cases  where  actual  firing  takes  place,  it  may  be  assumed  that  the 
heat  generated  in  the  stack  is  greater  than  that  dispersed  by  radiation.  Thus  the 
temperature  rises  till  the  ignition  point  is  reached.  The  greater  liability  of  some 
coals  to  fire  is  due,  therefore,  not  to  the  sulphur  they  contain,  but  to  their  proclivities 
for  absorbing  oxygen  ;  and  the  greater  the  quantity  of  oxygen  absorbed,  the  greater 
will  be  the  tendency  to  fire.  The  heating  effect,  too,  is  probably  cumulative ;  for 
a  rise  in  temperature  increases  the  capacity  of  the  coal  for  taking  up  oxygen. 

MEANS  or  PREVENTION 

On  the  question  of  the  actual  cause  of  spontaneous  ignition  there  is  a  certain 
amount  of  uniformity  among  the  opinions  expressed,  but  the  same  cannot  be  said 
with  regard  to  the  best  means  of  preventing  its  occurrence.  Many  divergent  views  have- 
been  brought  forward.  In  the  reports  of  the  German  Gas  Association  a  Mariendorf 
engineer  is  found  strongly  advocating  ventilation  as  a  means  of  preventing  ignition,. 


GAS-MAKING   AND   OTHER   COALS  247 

but  his  views  are  contradicted  by  others,  who  infer  that  ventilation  actually  causes 
fire.  Again,  it  is  noticed  that  the  New  South  Wales  Commission  on  the  Spontaneous 
Combustion  of  Coal  in  Bulk  recommended  a  "  free  use  of  the  hose  pipe,"  whereas 
another  authority  points  out  that  the  use  of  water  is  likely  to  be  followed  by  serious 
results  and  possible  explosion,- especially  in  confined  stores.  Primarily,  then,  it  is 
necessary  to  find  out  the  conditions  actually  favourable  to  combustion.  In  the 
first  place,  there  seems  little  doubt  that  there  is  far  greater  liability  in  hot  weather 
than  in  cold.  With  regard  to  the  question  of  ventilation,  many  opinions  have  been 
expressed  ;  and  some  few  years  ago  it  was  quite  a  regular  practice  to  resort  to  such 
expedients  as  perforated  iron  pipes,  wickerwork  baskets  without  bottoms,  also  elabor- 
ate ventilating  shafts  of  brick  and  wood,  so  as  to  ensure  the  passage  of  a  good  strong 
current  of  air  through  the  heap.  Great  caution,  however,  is  necessary,  for  it  must 
be  borne  in  mind  that  when  once  a  fire  has  been  started  it  will  not  continue  to  burn 
unless  the  supply  of  oxygen  is  maintained ;  and  very  often  the  ventilating  shafts, 
by  the  formation  of  a  draught,  supply  the  necessary  oxygen  for  sustaining  and  aug- 
menting the  fire.  Unless  ventilation  is  thorough,  therefore,  it  is  liable  to  cause  great 
mischief.  Perhaps,  taking  everything  into  consideration,  it  may  be  wiser  to  adopt 
surface  ventilation  only. 

Owing  to  the  greater  tendency  of  some  coals  to  fire,  it  is  as  well  to  keep  the 
various  classes  in  distinct  heaps  as  far  as  possible.  Experience  has  shown  that  it  is 
inadvisable  to  stack  all  the  large  coal  in  one  heap  ;  for  probably,  owing  to  disinte- 
gration, a  "  dust-pocket  "  will  be  formed  somewhere  towards  the  bottom.  The 
spaces  between  the  lumps  afford  excellent  opportunities  for  the  creation  of  a  draught, 
and,  consequently,  a  steady  supply  of  air  to  the  pocket.  In  such  a  case  we  get  con- 
ditions similar  to  those  occurring  with  insufficient  artificial  ventilation.  The  heap 
should  be  piled  so  that  lump  and  fine  are  distributed  as  evenly  as  possible.  A  point 
which  usually  escapes  observation  is  the  tendency  of  the  large  lumps  (when  tipping 
on  the  apex  of  a  heap)  to  run  to  the  outside,  leaving  the  centre  of  the  heap  composed 
of  slack.  This  is  undesirable,  and  the  coal  should  be  spread  out  as  the  heap  is  built 
up.  English  coal  spread  out  in  this  way  was  stacked  at  Berlin  to  a  height  of  46  feet 
for  more  than  twelve  months,  and  no  trouble  was  experienced  with  it.  The  depth 
of  the  heap  is  another  point  which  has  received  a  good  deal  of  attention.  According 
to  information  available,  it  appears  that  there  is  some  relation  between  the  liability 
to  spontaneous  combustion  and  the  height  and  volume  of  the  heap  in  which  it  occurs. 
There  also  appears  to  be  a  "  critical  height  "  above  which  it  is  inadvisable  to  go,  and 
for  ordinary  coals  this  ranges  between  15  and  20  feet.  Excessively  high  heaps  should, 
of  course,  be  avoided  as  far  as  possible,  for  pulverization  is  sure  to  take  place  towards 
the  bottom. 

DEALING  WITH  A  BURNING  HEAP 

The  undue  heating  of  a  coal  heap  is  usually  accompanied  by  "  steaming  "  and 
an  offensive  smell,  due  to  the  escaping  hydrocarbon  vapours.  When  these  are 
noticed,  the  usual  procedure  is  to  turn  the  hose  on  to  the  apparent  seat  of  the  trouble 
and  drown  out  the  fire.  When  a  fire  does  occur,  however,  it  is  necessary  to  avoid 


248  MODERN   GASWORKS   PRACTICE 

the  use  of  water  until  the  area  actually  affected  has  been  located.  The  coal  round 
about  this  area  should  then  be  dug  out,  and  the  smallest  possible  quantity  of  water 
made  use  of.  By  far  the  best  practice  is  to  get  the  affected  coal  away  to  the  retort 
louse  and  carbonize  it -as  soon  as  possible. 

A  coal  heap  should  be  kept  continually  under  observation.  The  most  usual 
means  of  recording  the  temperature  is  that  of  inserting  1J  to  2-inch  pipes,  one  end 
being  knocked  down  to  a  point.  A  thermometer — attached  to  a  cord — can 
then  be  lowered  into  the  pipes  and  the  temperature  noted.  As  the  drop  in  tem- 
perature while  the  thermometer  is  being  withdrawn  is  likely  to  be  somewhat  con- 
siderable, a  more  accurate  reading  will  be  obtained  if  a  maximum  thermometer  is 
used.  When  greater  accuracy  still  is  required,  it  is  necessary  to  use  a  low-tempera- 
ture pyrometer  with  electrical  connexions,  A  great  deal  of  trouble  will  be  saved 
if  the  temperature  pipes  are  suspended  in  position  before  the  heap  is  made,  for  the 
task  of  forcing  them  down  into  an  existing  heap  is  certainly  tedious.  An  idea 
from  America  is  that  of  a  coal  auger,  the  head  of  which  contains  a  small  maximum 
thermometer.  It  is  claimed  that  the  point  of  the  auger  can  be  driven  20  feet  in 
from  three  to  five  minutes,  and  about  ten  minutes  is  required  for  the  thermometer 
to  attain  the  temperature  of  the  surrounding  coal.  Temperatures  taken  in  this 
manner  have  been  found  to  be  40°  higher  than  by  the  pipe  method — the  difference 
being  ascribed  to  the  circulation  of  air  in  the  pipe.  When  the  temperature  rises 
above  90°  Fahr.,  the  upper  layers  of  coal  at  least  should  be  removed.  Disturbance 
of  the  heap  by  driving  in  rods,  etc.,  to  the  seat  of  the  fire  should  be  avoided,  for  this 
merely  has  the  effect  of  inducing  air  currents,  and  hence  provides  an  additional 
supply  of  oxygen.  When  a  fire  actually  breaks  out,  some  prefer  to  use  sand  instead 
of  water.  While  water  cools  the  material  and  reduces  the  temperature  below  ignition 
point,  sand  smothers  the  fire  and  cuts  off  the  supply  of  oxygen.  Sand  certainly 
recommends  itself  for  use  in  cases  in  which  the  action  of  water  is  known  to  have  a 
deleterious  effect  upon  the  surrounding  coal.  If  the  fire  were  large,  however,  it 
would  probably  afford  but  little  check. 

VERTICAL  RETORTS  AND  WET  COAL 

That  damp  coal  has  an  undesirable  effect  when  carbonized  in  ordinary  retorts 
is  indisputable.  In  works  in  which  there  are  chamber-ovens  or  vertical  retorts, 
the  moisture  matters  but  little.  Accordingly,  the  dry  coal  could  be  reserved  for 
the  horizontal  house,  while  the  wet  coal  could  be  disposed  of  in  the  verticals.  For 
some  unexplained  reason,  certain  coals  prove  themselves  particularly  liable  to  spon- 
taneous combustion  when  under  a  covering  of  snow.  Occasionally  fires  have  been 
caused  by  hot  pipes  which  run  through  the  heap  or  under  the  ground  upon  which  the 
coal  is  stacked.  Thus  it  appears  that  a  very  small  source  of  external  heat  is  sufficient 
to  start  the  action,  especially  if  the  heat  is  local  and  applied  towards  the  centre  of 
the  mass.  Another  point  is  that  of  the  local  application  of  water.  While  a  shower 
of  rain  seems  to  have  little  effect,  a  stream  of  water  confined  to  one  small  area  will 
probably  cause  a  rise  in  temperature.  This  is  best  illustrated  by  the  case  of  the 
covered  coal  store  with  a  leaky  roof,  and  the  fact  that  fires  frequently  occur  directly 


GAS-MAKING   AND   OTHER   COALS  249 

under  the  leak.     Leaky  water-pipes  in  the  vicinity  of  the  heap  very  often  lead  to 
trouble. 

Finally,  for  the  prevention  of  heating,  and  for  the  treatment  of  fires,  the  author 
suggests  the  following  points  : — 

1.  Stock  different  types  of  coal  in  separate  heaps. 

2.  Surface  ventilation  only. 

3.  Mix  lumps  and  fine  together.     Small  heaps  are  less  dangerous  than  large  ones. 

4.  Do  not  pile  to  a  greater  height  than  20  feet. 

5.  Avoid  external  sources  of  heat,  such  as  hot  pipes. 

6.  Attend  to  leaky  water-pipes  or  gutters  in  the  vicinity  of  the  heap. 

7.  When  temperature  rises  to  90°  Fahr.,  remove  top  layers  and  carefully  watch. 

8.  Do  not  disturb  the  fire  by  pushing  in  bars,  etc.,  from  the  side  of  the  heap. 

9.  Apply  water  to  the  seat  of  the  trouble  only,  particularly  if  fire  occurs  in 
confined  stores. 

10.  Remove  and  carbonize  the  affected  coal  as  soon  as  possible. 

DETERIORATION 

The  deterioration  of  coal  due  to  storage  is  another  vexed  question.  Though  all 
are  agreed  that  some  loss  does  take  place,  the  estimates  as  to  the  amount  vary  con- 
siderably. The  question  has  probably  received  far  more  attention  in  Germany  than 
in  this  country.  Herr  Prenger,  engineer  of  Cologne  gasworks,  has  found  that  the 
decrease  in  gas-making  value  of  English  coal  is  from  3  to  15  per  cent.,  or  an  average 
of  7  per  cent.,  when  stored  in  the  open,  and  from  0  to  10  per  cent.,  or  an  average  of 
4  per  cent.,  when  stored  under  cover.  Some  authorities  state  that  practically  no 
deterioration  occurs.  No  doubt  a  great  deal  depends  on  the  class  of  coal  in  question. 
The  coal  miners'  strike  of  1912  afforded  an  opportunity  of  gaining  some  experience 
on  the  subject,  and,  judging  by  working  results,  those  coals  which  had  been  lying 
in  stock  for  some  years  undoubtedly  yielded  less  gas,  less  ammonia,  and  a  rather 
inferior  coke — the  coke  giving  a  greater  proportion  of  breeze.  The  loss  in  calorific 
value  appears  to  be  quite  slight,  although  the  heating  value  of  the  coke  is  reduced 
in  some  cases.  This  usually  makes  itself  felt  in  the  percentage  of  coke  used  as  fuel. 
The  results  of  some  experiments  carried  out  on  the  coal-testing  plant  at  the  Saltley 
gasworks  of  the  Birmingham  Corporation  by  Dr.  Davidson  showed  that  the  gas 
multiples  for  coals  which  had  been  stocked  for  periods  of  six  months  to  two  years 
were  in  every  case  lower.  No  definite  loss  per  annum  is  fixed  by  the  tests,  but  it 
would  appear  to  be  no  more  than  2  per  cent.  The  experiments  showed  that  while 
the  gas  value  decreased  the  liquor  increased  very  appreciably  ;  but  the  coke  was 
markedly  inferior.  The  following  figures  are  those  given  by  a  well-known  English 
gas  coal  which  was  tested  after  the  intervals  stated  : — 

On  arrival  ......... 

After  3  months  .          .          .          .          . 

,,     5        „  . 

6 


Moisture. 
.     2-71' 

Make  per  ton. 
Cubic  feet. 
11,818 

.     5-22 

10,708 

.     5-64 

9,780 

.     7-58 

9,630  . 

250  MODERN   GASWORKS   PRACTICE 

THE   STORAGE   OF  COAL 

The  ideal  state  of  affairs  on  a  gasworks  would,  of  course,  be  to  take  in  just  as 
much  coal  as  is  required  for  present  requirements,  so  as  to  avoid  any  necessity  for 
keeping  a  stock  in  hand.  Owing,  however,  to  the  fluctuating  output  of  gasworks, 
and  to  the  fact  that  collieries  turn  out  an  amount  which  is  fairly  constant  all  the  year 
round,  these  conditions  are  impossible.  Moreover,  in  some  cases  a  reduction  in 
price  may  be  obtained  for  coal  delivered  during  the  summer  months  ;  and  many  gas 
companies  are  eager  to  seize  upon  this  opportunity.  In  respect  to  coal  deliveries,, 
the  United  ^Kingdom  is  more  fortunate  than  many  other  countries.  In  Germany, 
for  instance,  some  works  are  obliged  to  take  the  whole  of  their  coal  during  the  summer 
season,  owing  to  waterways  being  closed  by  frost  throughout  the  greater  part  of 
the  winter.  In  the  same  country,  too,  stored  coal  is  liable  to  deteriorate  to  a  far 
greater  extent,  owing  to  the  wider  variations  of  temperature  and  fluctuations  of 
weather  conditions. 

At  the  present  day  far  more  coal  is  stacked  out  in  the  open  than  in  elaborate 
stores,  such  as  were  erected  as  part  of  the  retort  house  on  nearly  all  works  in  years 
gone  by.  There  are  still,  however,  many  believers  in  the  indoor  method  ;  and  there 
is  no  doubt  that  coals  deteriorate  to  a  much  less  extent  when  sheltered  from  the 
weather.  The  opinion  is  expressed  by  some  engineers  that  coals  are  just  as  likely 
to  heat  up  under  cover,  and  when  they  do  so  they  are  far  more  difficult  to  get  at. 
Under  any  circumstances,  care  should  be  taken  to  see  that  the  store  is  not  situated 
too  near  to  the  heat  of  the  retort  bench.  It  is  with  stores  of  the  closed  type  that 
particular  care  is  necessary  with  regard  to  the  use  of  water.  When  coal  is  stacked 
in  a  bin  and  takes  fire,  the  application  of  water  to  the  red-hot  carbon  will  in  all  prob- 
ability be  followed  by  the  formation  of  water  gas.  This  gas,  in  addition  to  being  a 
source  of  danger  to  the  men,  owing  to  its  poisonous  nature,  may  mix  with  a  sufficient 
quantity  of  air  to  form  an  explosive  mixture,  which  might  conceivably  result  in  the 
destruction  of  the  bin.  When  coal  is  stored  in  covered  bins  some  arrangement  should 
be  provided  by  means  of  which  the  affected  layers,  which  are  frequently  at  the  base 
of  the  heap,  may  be  summarily  removed.  For  this  reason  the  more  recent  practice  of 
constructing  a  small  tunnel  from  end  to  end  of  the  store  and  below  floor  level  is  to 
be  strongly  advised.  The  tunnel  is  made  sufficiently  large  to  take  a  conveyor,  and 
by  means  of  pouches  fitted  with  sliding  doors  placed  at  frequent  intervals  the  coal 
in  the  affected  area  can  be  quickly  removed  and  carbonized.  An  arrangement  of 
this  nature  is  seen  in  Fig.  188. 

THE  STOEAGE  OF  COAL  UNDER  WATER 

Owing  to  the  tendency  of  stored  coal  to  fire  the  practice  of  submerging  the 
heaps  in  water  has  recently  been  adopted.  In  such  cases  special  reservoirs,  usually 
constructed  of  reinforced  concrete,  are  required.  The  method  has,  so  far,  been  con- 
fined almost  solely  to  America  and  the  Continent.  When  submerged,  the  coal  is 
protected  more  adequately  than  if  it  were  housed  ;  and  no  matter  what  the  weather 
conditions,  the  variation  in  temperature  of  the  mass  will  be  comparatively  smalL 


GAS-MAKING   AND   OTHER   COALS  25$ 

It  is  now  generally  recognized  that  the  gases  occluded  in  the  pores  of  the  coal — more 
particularly  oxygen — are  indirectly  the  cause  of  heating  and  deterioration.  The 
escape  of  the  oxygen  should  therefore  be  arrested  as  far  as  possible.  By  immersing 
coal  and  keeping  it  continually  sealed  this  condition  is  fulfilled,  the  gases  being  more 
or  less  confined,  whilst  little  or  no  oxidation  takes  place.  Breaking  up  of  lumps, 
and  pulverization  are  also  considerably  reduced,  because  the  water  forms  a  cushion 
between  the  various  pieces,  thus  lessening  the  effect  of  the  movement  of  the  lumps 


FIG.  188. — COAL  STORE  TUNNEL  SHOWING  CONVEYOR  AND  POUCHES. 

one  on  another.  The  better  physical  condition  of  the  coal  is,  however,  probably  due, 
in  part,  to  the  absence  of  heat,  which  in  itself  is  to  a  great  extent  the  cause  of  the 
opening  out  and  disintegration  of  the  larger  pieces.  There  is  no  limiting  depth  for 
the  heaps  of  coal  when  immersed,  and  accordingly  a  considerable  saving  of  space 
can  be  effected  ;  in  fact,  by  adopting  the  wet  method  the  capacity  per  unit  of  ground 
area  could  be  easily  doubled.  The  most  undesirable  factor  in  connexion  with  the 
system  is  that  of  expense.  One  of  the  largest  reservoirs  for  storing  coal  in  this  way 
is  that  on  the  banks  of  the  Oder,  at  Stettin,  where  20,QOO  tons  may  be  submerged.. 


-252  MODERN   GASWORKS   PRACTICE 

Another  series  of  tanks  for  storing  coal,  at  Omaha,  U.S.A.,  are  22  feet  in  depth,  with 
the  side  walls  carried  on  piles.  Piles  are  also  driven  under  the  whole  of  the  floor 
area  at  a  pitch  of  5  feet,  and  are  capped  with  square  slabs  of  concrete  on  which  the 
floor  rests.  The  side  walls  of  concrete  are  about  2  feet  thick  at  the  top  and  4  feet 
6  inches  at  the  bottom,  whilst  the  concrete  floor  is  protected  from  the  bite  of  the 
coal  "  grab  "  by  means  of  embedded  rails. 

As  an  instance  of  the  immense  stocks  of  coal  held  in  reserve  on  gasworks  it  may 
be  mentioned  that  the  bunkers  at  the  Tegel  works  at  Berlin  are  over  half  a  mile  in 
length  and  are  capable  of  containing  nearly  a  million  tons  of  coal. 


THE  nature  of  the  primary  and  secondary  reactions  associated  with  the  carboniza- 
tion of  coal  in  closed  retorts  has  occupied  the  attention  of  the  scientist  and  investi- 
gator for  nearly  a  century  ;  yet,  although,  to-day,  we  are  in  a  position  to  understand 
several  of  the  more  perceptible  developments  accompanying  this  phenomenon,  there1 
still  remain  many  anomalies  on  which  light  has  to  be  shed.  The  results  of  carbon- 
ization, and  the  final  mode  of  existence  of  the  innumerable  products  yielded,  are 
materially  influenced  by  considerations  other  than  that  of  the  temperature  at  which 
distillation  occurs,  so  that  it  is  impossible  to  form  an  opinion  as  to  ultimate  effects 
until  the  exact  conditions  under  which  the  process  is  carried  out  are  known. 

The  distillation  of  coal  is  usually  characterized  as  "  destructive,"  but  the  term 
is  in  reality  a  misnomer,  owing  to  the  fact  that  it  implies  finality ;  this  only  being 
the  case  so  far  as  the  original  structure  and  substance  of  the  raw  material  are  con- 
cerned. The  distillation  of  coal  differs  from  that  of  a  complex  liquid  in  that  the 
treatment  of  the  latter  is  carried  out  in  a  number  of  stages,  depending  upon  the  original 
nature  of  the  substance  and  the  character  of  the  products  required.  With  the 
liquid,  "fractionation  "  essentially  occurs,  whereas  coal  is  dealt  with  in  a  single  stage, 
innumerable  products  being  simultaneously  evolved  and  no  attempt  being  made, 
in  the  first  instance,  to  separate  out  the  various  compounds.  A  further  fact  of 
interest  is  that  with  coal,  once  distillation  has  occurred,  there  is  no  possibility  of 
reproducing  the  original  substance  by  collecting  the  products  and  causing  them  to 
recombine.  In  the  case  of  a  complex  liquid,  however,  the  various  fractions  may  be 
remixed,  when  a  substance  more  or  less  in  accordance  with  the  original  substance 
will  result. 

The  four  fundamental  bases  of  which  the  coal  conglomerate  is  considered  to 
exist  are  fully  discussed  in  the  previous  chapter,  and  it  is  there  pointed  out  that  when 
subjected  to  distillation  each  of  these  bases  gives  rise  to  its  own  particular  degrada- 
tion products.  Lewes,  in  his  researches,  found  evidence  that  the  primary  decom- 
position of  the  coal  substance  accounts  for  the  various  constituents  in  the  following: 
manner  : — 

253 


MODERN   GASWORKS   PRACTICE 


Gaseous  Products. 

Liquids. 

Solids. 

Humus  bodies,  yield     .      . 

Carbon  monoxide 
Carbon  dioxide 
Methane 

Water 
Thin  tar 

Free  carbon 

Hesin  bodies,  yield               .     < 

Carbon  monoxide 
Carbon  dioxide 
Ethylene,    and    unsaturated 
hydrocarbons 

Water 
Rich  tar 

Free  carbon 
Pitch 

Hydrocarbons,  yield     . 

Methane,    ethane   and    other 
paraffins 

Heavier  tars 

Free  carbon 
Pitch 

Carbon  Residuum.     Unaffected  by  distillation 

In  the  study  of  carbonization  it  is  essential,  in  the  first  place,  to  distinguish 
between  the  primary  and  secondary  products  of  distillation,  and  to  bear  in  mind 
that,  in  spite  of  the  ultimate  gas  containing  about  50  per  cent,  of  hydrogen,  this 
element,  per  se,  is  not  evolved  from  the  coal  in  the  early  stages,  but  results  from  the 
degradation  of  carbon  and  hydrogen  compounds,  and  to  some  extent  from  the  pro- 
duction of  water  gas.  The  lowest  temperature  at  which  carbonization  occurs  varies 
between  570°  and  750°  Fahr.,  when  chiefly  hydrocarbons  of  a  condensible  nature 
are  evolved,  the  permanent  gas  yield  being  comparatively,  small.  At  such  tempera- 
tures primary  products  alone  would  be  expected,  but  even  at  this  stage  some  secon- 
dary decomposition  will  have  occurred,  so  that  a  series  of  products  of  a  purely  primary 
nature  will  not  be  found.  Low  temperature  distillation  in  the  absence  of  degrada- 
tion would  account  for  the  following,  which  constitute  the  true  primary  gas  : — 

1.  Water  vapour. 

2.  Carbon  dioxide  and  carbon  monoxide. 

3.  Hydrocarbons  of  the  paraffin  series. 

The  bulk  would  be  made  up  of  these,  whilst,  in  addition,  there  would  be  smaller 
quantities  of  : — 

4.  Unsaturated  hydrocarbons. 

5.  Ammonia. 

6.  Sulphuretted  hydrogen. 

A  large  proportion  of  the  paraffin  hydrocarbons  would  be  of  a  condensible 
nature,  accounting  for  tar  rich  in  the  methane  hydrocarbons.  From  the  above  it 
will  be  seen  that  the  water  vapour  and  oxides  of  carbon  are  the  first  products  to  be 
evolved,  and  that  of  the  primary  constituents  methane  is  by  far  the  most  important. 

THE  ELEMENTS  IN  COAL  AND  THEIR  RELATION  TO  CARBONIZATION 

Of  the  elements  in  coal,  carbon  is  present  in  the  greatest  proportion,  partly 
fixed  and  partly  capable  of  volatilization.  In  the  ordinary  way  from  15  to  20  per 


THE   CARBONIZATION   OF   COAL  255 

«ent.  of  the  total  is  present  in  the  "  free  "  state,  and  the  actual  distribution  has 
been  shown  to  be  somewhat  as  follows  : — 

DISTRIBUTION  OF  CARBON  IN  COAL 

<o)  As  hydrocarbons       . 8  per  cent,  of  total  carbon. 

(6)  As  carbon  monoxide  and  dioxide       .  .       .       ...          .          •     2—3       „  ,,  ,, 

(c)  As  tar       .          .         *         .         .         .         .          .  .8  „  „  ,, 

{d)  Remaining  in  coke    ......  .     80-85   „  ,,  „ 

{e)  Other  sources,  such  as  "scurf"          .         .          .          .          .1  ,,  „  ,, 

From  the  gas-making  point  of  view  the  carbon  and  hydrogen  are  the  two  most 
important  constituents.  The  hydrogen  passes  off  partly  in  combination  with  oxygen 
as  steam,  and  partly  combined  with  carbon  to  form  hydrocarbons  of  both  the  saturated 
and  unsaturated  series.  By  far  the  largest  quantity,  however,  is  found  as  free 
hydrogen  in  the  gas.  A  certain  proportion  of  the  hydrogen  remains  behind  in  the 
coke,  but  with  the  modern  tendency  to  conduct  carbonization  at  extremely  high 
temperatures,  little  can  withstand  the  final  stages  of  the  period,  and  the  amount 
so  remaining  seldom  exceeds  0-5  per  cent. 

Although  the  solid  residue  left  behind  in  the  retort  contains  a  greater  proportion 
of  carbon  and  less  hydrogen  than  the  original  coal,  the  reverse  is  the  case  with  the 
volatile  portion,  which  shows  a  preponderance  of  hydrogen.  The  constitution  of 
this  volatile  portion  largely  depends  upon  the  temperature  prevailing.  As  a  general 
rule  the  volume  of  permanent  gas  obtained  is  in  direct  ratio  to  the  temperature 
employed,  whilst  the  quality  varies  inversely  with  the  temperature.  Of  the  carbon 
and  hydrogen  compounds,  those  evolved  at  the  lower  temperatures  of  carbonization 
are  mostly  condensible  at  ordinary  temperatures,  and  the  permanent  gas  obtained 
consists  mainly  of  methane,  ethane  and  ethylene  ;  that  is  to  say,  hydrocarbons  of 
the  paraffin  and  olefiant  series.  In  addition,  a  small  proportion  of  hydrogen  due 
to  secondary  reaction  will  be  present.  The  liquid  products  will  be  largely  of  a 
paraffinoid  nature.  It  is  during  the  early  stages  of  carbonization  that  the  more 
valuable  constituents  are  evolved,  and  as  the  temperature  throughout  the  entire 
mass  gradually  rises  to  the  present  limit  of  about  2,000°  Fahr.  the  volatile  products 
are  composed  mainly  of  methane  and  hydrogen,  the  proportion  of  the  former  diminish- 
ing and  of  the  latter  increasing  as  the  period  proceeds,  until  finally  little  more  than 
the  residual  hydrogen  and  nitrogen  of  the  coke  remain  to  be  expelled.  Owing  to 
the  thickness  of  the  modern  heavy  charge  the  heat  penetrates  to  the  interior  of  the 
mass  comparatively  slowly  ;  accordingly  hydrocarbons  and  gases  of  a  primary 
nature  are  continuously  being  evolved  until  the  central  cool  core  is  carbonized 
through.  Portions  of  these  primary  gases,  however,  only  exist  momentarily.  They 
undergo  degradation  into  simpler  compounds  on  coming  into  contact  with  the  heated 
coke,  and  are  further  decomposed  whilst  travelling  along  the  free  space  to  the  outlet 
of  the  retort.  For  this  reason  it  is  advantageous  to  distinguish  between  not  only 
primary  and  secondary  products,  but  also  between  primary,  secondary  and  tertiary 
effects.  That  is  to  say,  to  consider  the  ultimate  substances  obtained  to  consist 
of:— 


256  MODERN   GASWORKS   PRACTICE 

(a)  True  primary  products  escaping  further  degradation. 

(6)  Secondary  products  resulting  from  decomposition  due  to  passage  through 
the  hot  coke  mass. 

(c)  Tertiary  products  resulting  from  the  further  degradation  of  secondary  pro- 
ducts owing  to  the  exposure  of  the  latter  to  radiant  heat  and  to  hot  surfaces  during 
their  passage  from  the  retort. 

It  is  the  hydrocarbons  of  both  the  saturated  and  unsaturated  series  which  are 
chiefly  affected  by  these  further  influences,  but  oxygen-bearing  substances  and 
nitrogen  compounds  also  undergo  some  change. 

In  addition  to  being  present  in  the  coal  substance,  oxygen  is  derived  in  some 
quantities  from  the  moisture  in  coal,  the  latter  varying  from  4  to  10  per  cent.  This 
moisture  is  in  the  main  detrimental  to  the  process  of  carbonization,  in  that  it  tends 
to  reduce  the  temperature  of  the  retort  owing  to  the  large  quantity  of  latent  heat 
absorbed  in  converting  the  water  into  steam.  In  the  earlier  stages  the  oxygen  of 
the  coal,  as  distinct  from  that  emanating  from  the  moisture,  is  evolved  largely  as 
oxides  of  carbon,  whilst  on  combination  with  the  hydrogen  some  portion  will  give 
rise  to  water.  Colman  is  of  the  opinion  that  the  oxygen  is  originally  evolved  as 
volatile  compounds  of  carbon,  hydrogen  and  oxygen,  and  that  these  on  further 
heating  are  decomposed  into  carbon  monoxide,  carbon  dioxide  and  steam.  Whatever 
the  manner  of  formation  of  the  oxides  of  carbon,  however,  it  is  quite  evident  that 
the  carbon  dioxide,  during  its  passage  through  the  outer  coke  layers,  tends  to  combine 
with  the  red-hot  carbon,  undergoing  conversion  into  carbon  monoxide.  In  this  way 
secondary  reaction  is  responsible  for  an  increase  in  the  combustible  gases  at  the 
expense  of  an  inert  and  useless  diluent.  The  greater  the  temperature  of  distillation 
the  more  pronounced  will  this  interchange  be. 

Of  the  oxygen  present  in  coal  the  greater  portion  combines  with  hydrogen  to 
yield  steam,  about  25  per  cent,  exists  as  oxides  of  carbon,  and  a  small  proportion  is 
found  as  compounds  of  hydrogen  and  carbon,  such  as  the  phenols,  etc.,  in  the  tar. 
So  far  as  the  steam  derived  both  from  the  original  moisture  in  the  coal  and  from 
the  direct  combination  of  hydrogen  and  oxygen  is  concerned,  the  greater  proportion 
of  this  will  eventually  condense  out  as  water,  whilst  some  portion  will  account 
for  the  formation  of  water  gas  during  its  passage  through  the  heated  coke.  It  will 
be  seen,  accordingly,  that  the  importance  attached  in  the  past  to  the  "  unoxidized 
hydrogen  "  content  of  a  coal  was  much  over-estimated,  for  an  appreciable  portion 
of  the  oxygen  of  the  coal  substance  is  disposed  of  in  other  ways  than  by  direct 
combination  with  hydrogen. 

THE  NITROGEN  OF  COAL 

The  element  nitrogen,  although  of  more  or  less  subsidiary  importance,  enters 
materially  into  the  reckoning  when  the  economics  of  carbonization  come  to  be  con- 
sidered. The  aim  of  the  gas  engineer  must  be  to  recover  in  the  most  valuable  form 
the  largest  possible  proportion  of  the  total  nitrogen  present,  which  on  further  treat- 
ment forms  the  basis  of  one  of  his  most  valuable  by-products,  sulphate  of  ammonia. 
The  amount  of  nitrogen  in  bituminous  coals  is,  on  the  whole,  the  least  variable  of 


THE   CARBONIZATION   OF   COAL  257 

any  of  the  constituents,  the  figure  fluctuating  but  little  on  either  side  of  14  per  cent. 
This  percentage  corresponds  with  a  yield  of  about  34  Ib.  of  nitrogen  per  ton  of  coal 
employed,  whilst  the  average  yield  of  sulphate  of  ammonia,  amounting  to  27  Ib. 
per  ton,  represents  a  quantity  of  ammonia  equal  to  7  Ib.,  or  about  one-sixth  of  the 
total  nitrogen.  In  addition,  a  small  portion  may  be  usefully  recovered  in  the  form 
of  cyanide  compounds ;  but  comparatively  few  gasworks  are  provided  with  the 
necessary  plant  for  this  purpose.  For  some  years  attention  has  been  directed  towards 
the  possibility  of  recovering  a  greater  proportion  of  the  original  nitrogen,  but  although 
plants  for  the  production  of  low-grade  gas  are  operating  successfully  in  this  direction, 
the  conditions  under  which  the  increased  yield  is  obtained  are  scarcely  consistent 
with  ordinary  gasworks  methods.  As  an  instance,  mention  may  be  made  of  the 
Mond  gas  apparatus,  by  means  of  which  an  average  yield  of  96  Ib.  of  sulphate  of 
ammonia  is  obtained,  this  quantity  representing  nearly  25  Ib.  of  recovered  ammonia, 
or  about  65  per  cent,  of  the  total  nitrogen. 

One  of  the  earliest  attempts  to  determine  the  relative  quantities  in  which 
nitrogen  is  distributed  among  the  various  products  was  made  by  Foster,  in 
1883.  This  investigator  employed  a  Durham  coal  containing  1-73  per  cent,  of  nitro- 
gen, and  the  conclusions  arrived  at  are  as  follows  : — 

Nitrogen  remaining  in  coke      .          .          .  ,  .     48-68  per  cent,  of  total. 

„        free  in  gas  and  combined  in  tar  .  .     35-26           „  „ 

„        as  ammonia       ...          .          .  *»•  .     14-50           „  „ 

„        as  cyanogen       .          .          .          ,  .  .1-56           „  „ 

Investigation  of  this  kind  is  attended  by  considerable  difficulties,  and  several 
other  workers  have  derived  figures  on  the  same  lines,  but  in  no  case  are  they  in  close 
agreement.  The  researches  of  McLeod,  conducted  in  1907,  are,  however,  considered 
most  trustworthy,  having  been  carried  out  under  everyday  conditions.  McLeod's 
figures  are  as  follows  : — 

Nitrogen  in  coke      .  .         .         .  .  ,  .  .  .58-3  per  cent. 

„        free  in  gas  .                    .  -   .  .  .  .     19-5         „ 

„        as  ammonia  ..'..•..  .  .  .  .  .     17-1         „ 

„       as  tar       .  „  .        ..         .  .  .  .  .  .       3-9        „ 

„        as  cyanogen  ....  .  •    ' '.  .  .  .       1-2         „ 

The  figures  which  Short  obtained  for  conditions  existing  in  coke  ovens  are 
instructive,  in  that,  with  the  present  tendency  towards  mass  carbonization  in  gas- 
works, they  probably  approach  more  nearly  the  actual  state  of  affairs.  Short's 
researches  show  the  following  distribution  : — 

Nitrogen  in  coke      .  .  .'  .  .  .  ..''  .  .     43-3  per  cent. 

„  tar        .  .  .  .  ...  ..  ..  .  .       3-0        „ 

,,         „  ammonia  .  .  .  .  .  .  .     15-2         „ 

„         ,,  cyanogen  .  .  .  .  .  •  .       1-4         „ 

Free  nitrogen  in  gas  .  .  .  .  .  .  .  .37-1         „ 

In  all  cases  the  results  conclusively  show  that  by  far  the  greater  proportion  of 
nitrogen  remains  behind  in  the  coke  ;  but  with  the  prolonged  periods  and  high 
temperatures  of  modern  distillation  methods  the  proportion  remaining  in  the  solid 

s 


258  MODERN   GASWORKS   PRACTICE 

residue  is  undoubtedly  far  less  than  was  the  case  some  few  years  ago.  The  effect  of  a 
long-sustained  heat  such  as  exists  with  the  present-day  12-hour  charge  was  shown  by 
Watson  Smith  to  be  conducive  to  the  most  complete  expulsion  of  the  nitrogen  from 
the  coke,  and  he  found  in  the  case  of  coke-oven  coke  (which  is  essentially  subjected 
to  this  type  of  heating)  that  the  nitrogen  percentage  was  only  0-384. 

It  would  appear  that  in  all  cases  the  figures  given  for  the  nitrogen  distributed 
as  cyanogen  are  considerably  below  those  prevailing  in  modern  practice.  At  the 
present  time  there  are  many  cyanogen  plants  at  work  recovering  on  an  average 
from  4  to  5  Ib.  of  ammonium  sulphocyanide  per  ton  of  coal,  these  quantities  of 
sulphocyanide  representing  from  0-75  to  1  Ib.  of  nitrogen,  or  nearly  3  per  cent,  of  the 
total  nitrogen.  As  nitrogen,  however,  is  drawn  in  from  the  atmosphere  and  furnace 
it  is  possible  that  a  portion  of  the  nitrogen  combined  in  the  cyanogen  is  obtained 
from  such  external  sources.  The  nitrogen  combined  in  tar  is  chiefly  present  in  the 
form  of  nitrogenous  bases  such  as  pyridine. 

It  will  be  realized  that  if  it  were  possible  to  recover  the  whole  of  the  original 
nitrogen  in  coal  as  sulphate  of  ammonia  the  yield  of  sulphate  would  approximate 
to  180  Ib.  per  ton  of  coal  carbonized. 

A  good  deal  of  uncertainty  exists  as  to  the  type  of  coal  wyhich  is  likely  to 
prove  the  most  efficient  producer  of  ammonia.  Schilling,  for  instance,  says  that  the 
amount  of  ammonia  yielded  rises  and  falls  according  to  the  quantity  of  nitrogen  in 
the  coal.  Knublauch  is  of  the  opinion  that  the  coals  which  give  very  high  yields 
of  gas  and  tar  have  a  tendency  not  to  form  ammonia,  the  hydrogen  uniting  with 
the  carbon,  whilst  the  coals  which  account  for  high  ammonia  yields  show  an 
inclination  to  leave  the  nitrogen  in  the  coke  and  not  to  form  free  nitrogen  in  the 
gas.  More  important  considerations,  however,  do  not  permit  of  a  coal  being 
purchased  on  its  nitrogen-yielding  proclivities  alone. 

With  regard  to  the  formation  of  ammonia,  there  is  now  little  doubt  that  it  is 
the  direct  result  of  two  distinct  reactions,  and  that  whereas  the  chief  of  these  takes 
place  at  lower  temperatures,  the  second  is  probably  most  in  evidence  at  higher  heats. 
Accordingly,  ammonia  resulting  from  distillation  may  be  formed  : — 

(a)  By  direct  evolution  from  an  ammonia  yielding  body  contained  in  the  coal. 

(6)  Synthetically,  by  the  combination  of  hydrogen  and  residual  nitrogen. 

Little  is  known  as  to  the  actual  mode  of  existence  of  the  nitrogen  compounds 
in  coal,  but  there  is  evidence  to  show  that  the  element  is  combined  in  two  or  more 
ways.  Lewes  is  of  the  opinion  that  the  humus  bodies  are  most  likely  to  be  those 
carrying  the  nitrogen.  So  far  as  the  coke  is  concerned,  Harger  says  the  only  con- 
clusion he  could  arrive  at,  after  careful  consideration  of  all  the  facts,  was  that  some 
of  the  nitrogen  in  the  coke  is  present  as  one  or  more  stable  organic  nitrogen  ring 
compounds. 

Under  the  influence  of  distillation  ammonia  is  one  of  the  first  compounds  to  be 
expelled,  the  evolution  commencing  at  temperatures  between  600°  and  750°  Fahr., 
and  continuing  up  to  about  1,000°  Fahr.,  when  the  whole  of  the  primary  portion 
appears  to  be  evolved.  Little  or  none  is  given  off  as  the  temperature  rises  from 
1,000°  Fahr.  to  1,600°  Fahr..  but  beyond  the  higher  temperature  further  appreciable 


THE   CARBONIZATION   OF   COAL  259 

quantities  are  discernible.  Accordingly,  the  maximum  yield  of  ammonia  is  obtained 
only  when  the  distillation  temperature  has  reached  1,600°  Fahr.  or  slightly  over. 
The  possibility  of  an  easily  decomposible  compound  being  able  to  exist  at  this  tem- 
perature is  explained  by  the  fact  that  if  an  unstable  gas  be  diluted  with  some  con- 
siderable quantity  of  inert  gas  the  temperature  necessary  to  bring  about  decompo- 
sition increases  rapidly  in  proportion  with  the  amount  of  dilution.  Thus  the  ammonia 
is  quickly  exhausted  away  from  the  retort  before  feeling  the  effects  of  degradation. 
It  is  in  this  manner  that  the  high  yield  of  ammonia  in  the  Mond  plant  may  be 
explained,  for  an  excess  of  steam  and  air  is  admitted  to  the  base  of  the  fuel  bed 
and  forms  an  enveloping  gaseous  mass  (containing  a  high  percentage  of  inert 
constituents)  which  shields  the  ammonia  on  its  passage  through  the  producer. 

The  production  of  the  secondary  ammonia,  as  distinct  from  that  evolved  as 
a  primary  compound,  has  been  explained  by  Tervet,  who  states  that  a  portion  of 
the  nitrogen  remaining  in  the  coke  can  be  liberated  in  the  form  of  ammonia,  so  long 
as  the  ammonia  is  brought  into  a  state  of  strain  which  shall  prevent  it  from  sub- 
sequent degradation.  This  state  is  effected  by  subjecting  the  ammonia  to  the 
superior  affinity  which  exists  between  the  combined  nitrogen  in  the  coke  and  free 
hydrogen  at  a  particular  temperature  and  in  a  diluting  atmosphere.  Thus  synthesis 
between  the  free  hydrogen  in  the  retort  and  the  nitrogen  evolved  from  the  coke  at 
higher  temperatures  is  taking  place. 

Important  work  on  the  question  of  the  effect  of  temperature  and  other  con- 
ditions on  the  yield  of  ammonia  has  recently  been  carried  out  by  Cobb  and  Rollings, 
who  are  still  engaged  in  the  research.  In  their  experiments  these  investigators  have 
studied  the  decomposition  of  the  ammonia  from  coal  when  the  products  are  sub- 
jected to  differing  conditions.  In  each  case  a  small  quantity  of  coal  was  distilled 
in  a  boat  contained  in  a  specially  sealed  and  heated  tube,  and  the  ammonia  present 
in  the  products  was  estimated.  The  gases  evolved  from  the  coal  were  first  drawn 
away  from  a  tube  which  was  so  designed  and  arranged  that  secondary  reaction  had 
no  time  to  exert  its  influence  ;  in  the  second  series  of  experiments  they  were  drawn 
through  a  heated  tube  and  subjected  to  radiant  heat ;  whilst,  thirdly,  the  tube  was 
packed  with  coke,  and  the  gases  drawn  through  this.  The  results  of  their  experiments 
may  be  briefly  tabulated  as  follows  : — 

(a)  Minimum  heat  action     .         .22-5  per  cent,  of  nitrogen  in  coal  recovered  as  ammonia. 
(&)  Gases  subjected  to  radiant  heat  17-2  ,,  „  „  „  „ 

(c)  Gases  passed  through  hot  coke     9-4  „  „  „  „  „ 

From  these  figures  conclusions  can  be  drawn  as  to  the  effect  of  high  tempera- 
tures and  travel  over  heated  surfaces  on  the  yield  of  ammonia.  The  temperature 
of  800°  C.  (1,470°  Fahr.)  was  used  throughout. 

The  effect  of  the  heavy  charge  of  long  duration  in  ensuring  the  gases  being 
swept  from  the  retort  before  decomposition  has  occurred  to  any  extent  is  shown  by 
the  following  figures  given  by  Ferguson  Bell : — 

6- hour  charges  of    6  cwts.  of  coal,  yield  of  ammonia  7-26  Ib.  per  ton. 
8-hour          „  7|     „  „  „  „          8-26    „ 

10-hour          „  9J     „  „  „  „         8-45     „ 

12-hour          „          11 1    „          „  „  „         8-50    „ 


260  MODERN   GASWORKS   PRACTICE 

The  small  portion  of  the  original  nitrogen  of  the  coal  which  is  found  as  cyanides 
is  almost  wholly  in  the  form  of  hydrocyanic  acid,  although  small  quantities  of  free 
cyanogen  are  also  present.  Hydrocyanic  acid  is  essentially  a  high  temperature 
product,  and  probably  makes  no  appearance  in  the  retort  below  temperatures  of 
1,600°  to  1,700°  Fahr.  When  higher  temperatures  were  first  introduced  in  con- 
junction with  the  light  6-cwt.  coal  charge  a  distinct  increase  in  the  yield  of  cyanogen 
was  noticeable,  whilst  the  yield  of  ammonia  showed  some  falling  off.  There  seems 
little  doubt  that  the  greater  portion  of  the  cyanogen  is  produced  at  the  later  stages 
of  the  charge,  when  the  temperature  is  at  a  maximum,  and  the  traces  of  syntheti- 
cally produced  ammonia  which  may  be  coming  away  have  few  diluent  gases  to  shield 
them  from  decomposition.  It  is  at  these  higher  temperatures  that  a  portion  of  the 
ammonia  is  split  up  into  its  elements  hydrogen  and  nitrogen  which  react  with  carbon 
and  yield  hydrocyanic  acid.  It  does  not  necessarily  follow,  however,  that  a  high 
yield  of  cyanogen  means  a  decreased  production  of  ammonia,  and  in  many  cases 
a  high  yield  of  both  products  is  obtained. 

Some  investigators,  such  as  Kulmann,  have  shown  that  if  carbon  monoxide  and 
ammonia  are  passed  over  spongy  platinum  a  small  quantity  of  hydrocyanic  acid  is 
formed,  and  this  has  led  to  the  supposition  (probably  erroneous)  that  cyanogen 
may  be  formed  in  some  degree  by  the  double  decomposition  of  carbon  monoxide 
and  ammonia.  Others  support  the  theory  that  ammonia  and  carbon  disulphide 
react  to  form  the  product.  It  must  be  remembered  that,  like  ammonia,  hydro- 
cyanic acid  itself  is  liable  to  decomposition  at  the  higher  temperatures,  and  that 
the  quantities  in  which  it  is  ultimately  found  probably  depend  to  some  extent 
upon  the  amount  of  diluent  gases  which  conduct  it  safely  from  the  retort. 

As  regards  the  decomposition  of  ammonia,  Bueb  carried  out  a  series  of  ex- 
periments which  showed  that  at  temperatures  of  about  1,400°  Fahr.  approxi- 
mately 4  per  cent,  of  the  nitrogen  of  the  ammonia  was  converted  into  cyanogen, 
whereas  at  1,800°  Fahr.  nearly  one-quarter  of  the  amount  had  undergone  this 
change.  A  somewhat  remarkable  result  was  obtained  by  Cobb  and  Rollings  in 
connexion  with  hydrocyanic  acid.  In  the  experiments  previously  quoted,  after 
decomposition  of  ammonia  had  taken  place  the  products  were  tested  for  cyanogen, 
but  in  no  case  could  the  presence  of  this  compound  be  detected.  This  is  probably 
explained,  however,  by  the  fact  that  the  conditions  favourable  to  the  production  of 
cyanide  were  absent. 

Several  attempts  have  been  made  to  increase  artificially  the  recoverable  pro- 
portion of  the  total  nitrogen  in  coal,  but  their  measure  of  success  has  been  such  that 
the  suggested  methods  have  only  been  adopted  on  gasworks  in  isolated  instances. 
Among  them  may  be  mentioned  the  liming  of  coal,  originated  by  Cooper,  and  now 
in  constant  operation  at  the  Cheltenham  gasworks.  In  this  process  lime  is  charged 
with  the  coal  into  the  retorts.  In  order  that  thorough  admixture  may  take  place 
the  coal  is  slightly  damped  on  the  surface  by  a  steam  jet,  thus  causing  the  lime  to 
cling  to  the  lumps.  The  quantity  of  lime  intermixed  with  the  coal  is  usually  about 
2  per  cent.  As  a  result  of  its  employment  the  sulphate  of  ammonia  recovered  per 
ton  of  coal  carbonized  shows  an  average  increase  of  nearly  2  Ib.  The  improvement 


THE   CARBONIZATION   OF   COAL  261 

in  the  yield  of  ammonia  in  this  case  is  due  to  the  fact  that  admixture  of  a  caustic 
alkali  has  some  tendency  to  convert  the  residual  nitrogen  of  the  coke  into  ammonia. 
Some  thirty  years  ago  a  method  was  discovered  of  extracting  nitrogen  in  the 
form  of  ammonia  from  the  coke  of  shale  retorts,  by  passing  steam  through  the  fuel 
bed  whilst  in  a  highly  heated  condition.  In  this  way  the"  recovered  ammonia  in- 
creased by  about  200  per  cent.  Several  suggestions  were  made  for  the  application 
of  the  same  principle  to  the  recovery  in  the  form  of  ammonia  of  the  nitrogen  left 
behind  in  the  coke  produced  on  gasworks.  One  promising  suggestion  provided  for 
dropping  the  red-hot  coke  as  it  came  from  the  retorts  into  special  chambers  maintained 
at  a  high  temperature  into  which — for  a  short  period — steam  could  be  blown.  A 
certain  quantity  of  blue  water  gas  is  thus  obtained,  and  at  the  same  time  a  large 
additional  yield  of  ammonia.  Another  means  was  based  on  the  fact  that  when 
hydrogen,  or  a  gas  rich  in  hydrogen,  is  passed  through  highly  heated  coke  the  hydro- 
gen combines  with  the  latent  nitrogen  to  form  ammonia.  Such  conditions  are 
obtained  by  blowing  water  gas  into  the  retort  towards  the  end  of  the  charge.  This 
scheme  has  been  tried  on  several  wrorks,  and  is  now  in  operation  at  a  few.  The 
chief  objection  to  it  is  the  degree  to  which  the  illuminating  power  of  the  final  gas 
is  reduced.  So  far  as  gasworks  are  concerned  the  many  suggestions  for  recovering 
a  greater  proportion  of  the  nitrogen  of  coal  have  as  yet  led  to  no  satisfactory  result ; 
but  the  problem  is  of  deep  concern  to  the  gas  engineer  and  should  not  be  allowed 
to  rest. 

THE  SULPHUR  or  COAL 

A  portion  of  the  sulphur  present  in  the  coal  substance  is  of  a  more  or  less  "  fixed  " 
nature  and  remains  behind  in  the  coke.  This  portion  is  usually  present  in  the 
original  coal  as  calcium  sulphate,  whilst  the  volatile  sulphur  is  chiefly  derived  from 
pyrites  and  certain  organic  sulphur  compounds.  Coals  as  commonly  used  for  gas- 
making  contain  a  percentage  of  sulphur  varying  from  0-6  to  1-2,  and  that  remaining 
behind  in  the  coke,  under  modern  conditions  of  carbonization,  seldom  exceeds  0-8 
to  1  per  cent.  As  previously  pointed  out,  sulphuretted  hydrogen  is  a  primary  pro- 
duct of  distillation,  and  is  one  of  the  first  products  to  be  evolved.  Colman  says  that 
the  sulphur  probably  comes  off  in  the  first  place  as  volatile  compounds  of  carbon 
and  hydrogen,  and  that  these,  when  more  strongly  heated,  yield  sulphuretted 
hydrogen.  A  small  quantity  of  sulphur,  hydrogen  and  carbon  compounds  are,  how- 
ever, ultimately  obtained,  as  an  instance  of  which  may  be  mentioned  thiophen 
(C4H4S).  This  is  frequently  found  in  the  tar,  although  traces  of  it  are  usually 
present  in  the  small  percentage  of  sulphur  compounds  in  the  finished  gas. 

The  sulphur  compounds,  as  distinct  from  sulphuretted  hydrogen,  are  chiefly 
formed  at  the  higher  temperatures,  due  to  the  combination  of  part  of  the  sulphur 
with  carbon.  The  higher  the  temperature  of  distillation  the  greater  will  be  the 
quantity  of  sulphur  driven  off  from  the  coke,  and  extended  travel  of  the  gas  through 
heated  coke  or  in  contact  with  hot  surfaces  accounts  for  the  decomposition  of  sul- 
phuretted hydrogen  and  the  subsequent  formation  of  carbon  disulphide.  Accord- 


262  MODERN   GASWORKS   PRACTICE 

ingly,  when  secondary  reaction  at  high  temperatures  is  permitted  to  take  place 
the  easily  removable  sulphuretted  hydrogen  gives  place,  in  part,  to  undesirable 
compounds,  such  as  carbon  disulphide,  which  are  only  eliminated  from  the  gas  with 
great  trouble.  Sulphuretted  hydrogen  is  usually  present  in  the  crude  gas  in  the 
proportion  of  about  1-5  per  cent.,  whilst  the  other  sulphur  compounds  together  total 
no  more  than  0-05  per  cent. 

DISTRIBUTION  OF  ELEMENTS  IN  COAL  AND  GAS. 

Below  is  set  out  a  table  showing  the  approximate  distribution  of  the  elements 
in  a  ton  of  coal  and  the  manner  in  which  each  element  exists  after  the  process  of 
carbonization.  The  table  is,  of  course,  merely  illustrative,  and  does  not  do  more 
than  give  a  general  indication  of  the  lines  on  which  the  rearrangement  of  the  elements 
takes  place.  It  is  assumed  that  no  loss  has  taken  place  and  that  no  other  products 
have  been  introduced. 

1  Ton  of  coal. 

Consisting  of : — 

1,792  Ib.  carbon. 

Distributed  as  coke         .          ,      , 1,385    Ib. 

„          as  breeze       .........  107     „ 

„          in  gas,  as  CO,  and  CO2.          .....  30     „ 

„          in  gas,  as  hydrocarbons          .          .  .  .  .  130     „ 

„          in  tar  .          .          .          .          .          .  .  .  .  122     „ 

„          as  scurf,  cyanide,  etc.    .          .          .  .  .  .  18     „ 

123  Ib.  hydrogen. 

Distributed  in  gas  and  tar      .    <     .          .          .  .  .  .  98*5  „ 

„          as  ammonia.          .    -     ,          .          .  .  "  »  .  1-0  „ 

,,         as  water       .'         .         .  ."     .         .  •    '. :  .  18-5  „ 

„          in  coke        ' .         .       '.'. ,                 .  .  .  ,  5     „ 
197  Ib.  oxygen. 

Distributed  as  CO,  C02  and  combined  in  tar  .  .  .  .  49     „ 

„         as  water       .         .         .         .         .  ,  .  .  148     „ 

34  Ib.  nitrogen. 

Distributed  in  gas  (free)         ...          .          .          .  ..  .  .  ',  11-8,, 

,,          in  coke          .         .•        ...          .  ,  ,  '   .  14-1  „ 

„          in  tar  (combined).       •   .         .          .  .,  «  •  I'O  „ 

„          as  ammonia.          .         .          .         ,  .  ,  ,  .  5-8  „ 

„          as  cyanogen  (total  HCN  4  Ib.)       .  .  .  1-3  „ 
18  Ib.  sidphur. 

Distributed  as  gaseous  impurities  and  in  liquor  ...  6     „ 

,,          in  coke          .          ...          .  .  .  .  12     „ 

76  Ib.  ash  remaining  in  coke  and  breeze        .         .  .  ,  .  76     „ 


2,240  Ib.  2,240  Ib. 

The  yield  given  for  water  amounts  to  166£  lb.(148  Ib.  from  oxygen  and  18'5  from 
hydrogen),  this  being  equivalent  to  about  16  gallons  of  virgin  liquor.  No  allowance, 
however,  has  been  made  for  the  steam  which  is  converted  into  water  gas.  In  the 
ordinary  way,  from  10  to  12  gallons  of  condensed  water,  or  virgin  liquor,  are  obtained, 
the  remainder  being  decomposed  in  contact  with  the  hot  coke. 


THE   CARBONIZATION   OF   COAL 


263 


A  comparison  between  the  chemical  constitution  of  the  solid  substance  before 
and  after  distillation,  i.e.,  the  contrast  between  coal  and  coke,  is  shown  as  follows  : — 


Before  Distillation. 

COAL. 

80  per  cent. 
5-5 
8-8 
1-5 
0-8 
3-4 


carbon 

hydrogen 

oxygen 

nitrogen 

sulphur 

ash 


After  Distillation. 

COKE. 

88-0  per  cent. 
0-2 

traces  to  3-0 
2-0 
1-0 
5-8 


(very  variable) 


THE  HYDROCARBONS 

Before  studying  the  hydrocarbons  it  is  of  advantage  to  have  a  clear  concep- 
tion of  what  is  understood  by  the  valency  of  the  elements.  All  elements  have  a 
certain  power  of  combining  with  other  elements,  and  many  can  exert  this  power 
either  wholly  or  in  part.  When  chlorine  and  hydrogen  unite,  one  atom  of  the  chlorine 
combines  with  one  atom  of  hydrogen  to  give  a  molecule  of  hydrochloric  acid.  But 
when  oxygen  unites  with  hydrogen,  one  atom  of  oxygen  takes  up  two  atoms  of 
hydrogen.  Furthermore,  ammonia  is  composed  of  one  atom  of  nitrogen  in  con- 
junction with  three  atoms  of  hydrogen  ;  whilst  one  atom  of  carbon  is  capable  of 
combining  with  four  atoms  of  hydrogen  (e.g.  CH4).  Thus  one  atom  of  some  elements 
unites  with  one  atom  of  others,  some  take  up  two,  some  three,  and  so  on,  before  they 
are  fully  satisfied  or  "  saturated."  Once,  however,  the  requisite  number  has  been 
absorbed,  then  the  original  atom  can  unite  with  no  more.  Elements  differ  con- 
siderably as  to  their  powers  of  combination,  and  it  is  proposed  to  consider  briefly 
here  only  those  most  important  in  gas-making,  and,  chiefly,  the  combining  powers 
of  carbon  with  hydrogen,  oxygen  and  nitrogen. 

Carbon  is  "  tetravalent,"  i.e.,  one  atom  unites  with  four  atoms  of  a  "  mono- 
valent  "  element  or  two  of  a  "  divalent  "  element,  or  two  atoms  of  a  monovalent 
element  and  one  of  a  divalent  element. 

Hydrogen  is  monovalent,  i.e.,  one  atom  combines  with  only  one  atom  of  a 
monovalent  element. 

Oxygen  is  divalent. 
1  Nitrogen  is  trivalent. 

Carbon  is  tetravalent. 

Chlorine  is  monovalent.' 
1  Sulphur  is  divalent. 

Carbon  differs  from  other  elements  in  forming  an  abnormally  large  number 
of  compounds  with  hydrogen — called  hydrocarbons.  The  simplest  is  methane 
(CH4).  The  various  compounds  are  classified  as  "  saturated  "  and  "  unsaturated," 
according  as  to  whether  the  carbon  atoms  are  (owing  to  their  tetravalent  nature) 
fully  saturated  or  not.  When  hydrocarbons  are  arranged  in  order  of  molecular 
weights,  they  comprise  a  series,  each  member  of  which  contains  so  many  atoms 
of  carbon  and  hydrogen  more  than  the  preceding  member.  For  example  : — 

1  Nitrogen  and  Sulphur  have  varying  valencies. 


Methane,  CH4 
Ethane,     C2H6 
Propane,  C3H8 
Butane,     C4H10 
Pentane,  C5H12 


difference  CH2 
,,  CH2 
,  CH2 


etc. 


Such  a  series,  of  which  the  members  undergo  a  constant  and  gradual  variation, 
is  known  as  a  homologous  series,  and  the  several  members  are  denoted  as  homo- 
logues  of  one  another.  The  above  series,  it  will  be  seen,  can  be  expressed  by  the 
general  formula  CnH2Q  +  2-  The  chief  homologous  series  of  hydrocarbons  of 
assistance  in  studying  the  chemistry  of  carbonization  are  the  following  : — 

(1)  The  paraffin  series. 

(2)  The  olefmes,  or  ethylene  series. 

(3)  The  acetylenes. 

(4)  The  benzene  or  aromatic  series. 

The  more  important  members  of  these  series  are  given  below  : — 


I. 

II. 

III. 

IV. 

Paraffin  (CnH2n+  2) 

Olefines  (CnH2n) 

Acetylenes  (CnH2Q—  2) 

Benzenes  (CnH2n—  6) 

Methane,  CH4 

— 

— 

— 

Ethane,  C2H6 

Ethylene,  C2H4 

Acetylene,  C2H2 

Benzene,  C6H6 

Propane,  C3H8 

Propylene,  C3H6 

Allylene,  C3H4 

Tolnene,  C7H8 

Butane,  C4H10 

Butylene,  C4H8 

Crotonylene,  C4H6 

Xylene,  C8H10 

Pentane,  C6H12 

Amylene,  C5H10 

Etc. 

Etc. 

Etc. 

Etc. 

AROMATIC  AND  ALIPHATIC  COMPOUNDS. 

The  benzene  series  was  originally  called  the  aromatic  series,  owing  to  the  fact 
that  the  first  hydrocarbons  discovered  were  obtained  from  aromatic  balsams  and 
resins.  Thus  by  "  aromatic  derivatives  "  are  meant  compounds  related  to  the 
benzene  series.  The  term  aliphatic  or  "  fatty  "  derivates  has  reference  to  those 
substances  associated  with  1*he  paraffin  or  methane  series. 

STRUCTURAL  FORMULAE 

It  has  already  been  mentioned  that  carbon  is  a  tetravalent  element,  i.e.,  one 
atom  can  combine  with 

(a)  4  atoms  of  a  monovalent  element,  e.g.  CH4. 
(6)  2  atoms  of  a  divalent  element,  e.g.  C02. 

(c)  1  divalent  and  2  monovalent  atoms,  e.g.  COC12. 

(d)  1  trivalent  and  1  monovalent  atom,  e.g.  HON. 

With  the  exception  of  carbon  monoxide  (CO)  no  compound  containing  only  one 
carbon  atom  is  known  in  which  the  carbon  atom  is  combined  with  either  more  or 
less  than  four  monovalent  elements  or  their  valency  equivalent.  It  must  be  pointed 


THE   CARBONIZATION   OF   COAL 


265 


out,  however,  that  Professor  Bone  has  concluded  that  certain  residues  such  as  CH 
and  CH2  may  have  a  very  brief  existence  under  definite  influences. 

Many  cases  are  known  in  which  two  or  more  compounds  have  the  same  molecular 
formula,  but  differ  considerably  in  chemical  and  physical  properties.  For  instance, 
there  are  three  distinct  compounds  bearing  the  formula  C5H12,  and  two  having  the 
molecular  formula  of  C2H402.  Owing  to  the  differing  characteristics  of  these  sub- 
stances, it  is  only  natural  to  conclude  that  whilst  as  regards  the  number  of  atoms  of 
the  various  elements  composing  the  molecule  they  are  similar,  these  atoms  are 
differently  arranged  and  give  rise  to  a  variation  in  constitution.  On  this  account 
suitable  formulae  (known  as  structural  formulae)  have  been  devised  to  express 
more  clearly  the  behaviour  and  constitution  of  the  compound.  Instead  of  denoting 

H 

I 
methane  by  CH4we  can  write  H  —  C  —  H  >  and  C02  may  be  expressed  as  0=C=0. 


H 

In  each  case  it  is  seen  that  the  tetravalent  nature  of  carbon  is  shown  by  four  affinities 
or  bonds  exerting  an  attractive  force  between  it  and  the  other  atoms.  The  single 
valency  of  the  hydrogen  atoms  and  the  dual  valency  of  the  oxygen  atoms  are  also 
correctly  expressed.  Such  methods  of  indicating  the  constitution  of  chemical  sub- 
stances are  of  extreme  value  in  studying  the  degradation  of  the  less  stable  hydro- 
carbons during  the  distillation  of  coal  in  the  retort.  In  the  case  of  the  unsaturated 
compounds  the  carbon  atoms  are  assumed  to  exert  an  affinity  on  one  another,  thus 

H        H 


acetylene  (C2H2)  is  not   written 


C        C 


but  H  —  CEEC  —  H-      Thus 


double  or  treble  bonds  exist  between  the  carbon  atoms.  Compounds  such  as 
acetylene,  with  structural  formula?  on  the  same  lines,  are  known  as  open  chain 
compounds,  whereas  in  more  complicated  substances  a  closed  ring  may  result. 
Notable  instances  of  the  latter  are  the  benzene  and  naphthalene  rings  given  below. 

H  H  H 


, 

//  \ 
H—  -C  C  —  H  H—  C 

H_  /•*  r*     —  u  LJ  _ 

Ov  v^~  n     ~ 

V  / 

x 


\ 


\ 


C  —  H 


__  LJ 
M 


H 

Benzene  (C6H6) 


H  H 

Naphthalene  (C10H8) 


266 


MODERN   GASWORKS   PRACTICE 


Owing  to  the  impossibility  of  depicting  the  true  arrangement  of  such  com- 
pounds on  a  flat  surface  (the  actual  arrangement  taking  place  in  space)  some  prefer 
to  avoid  the  use  of  double  or  multiple  bonds  and  to  place  the  surplus  affinities 
within  the  ring.  Thus,  benzene  is  denoted  by — 


THE  DEGRADATION  OF  THE  HYDROCARBONS 

The  secondary  reactions  which  take  place  during  the  carbonization  of  coal  have 
been  the  subject  of  an  unusual  amount  of  research.  The  variable  and  complicated 
conditions  under  which  these  changes  occur,  however,  render  the  path  of  the  investi- 
gator extremely  difficult.  When  a  comparison  of  results  is  made,  therefore,  it  is 
not  surprising  to  find  the  expression  of  a  number  of  contradictory  opinions,  although 
with  regard  to  many  of  the  more  important  facts  a  certain  amount  of  uniformity  is 
displayed.  Primarily,  it  is  recognized  that  when  subjected  to  certain  severe  influ- 
ences many  of  the  less  stable  products  evolved  from  coal  are  unable  to  withstand  their 
tendency  to  decompose,  with  the  result  that  they  are  split  up  into  more  stable  com- 
pounds of  a  similar  nature.  This  degradation  or  reconstruction  chiefly  applies 
to  the  carbon  and  hydrogen  compounds,  although— as  previously  shown — substances 
(such  as  ammonia  and  carbon  dioxide)  composed  of  other  elements  are  by  no  means 
immune.  It  must  be  recognized  that  in  order  to  obtain  the  maximum  yield  of  gas 
from  a  definite  bulk  of  coal  it  is  not  sufficient  to  submit  the  solid  mass  alone  to  a 
very  high  temperature,  but  the  primary  volatile  products  must  afterwards  come 
under  the  influence  of  further  heat,  so  that  some  portion  of  the  condensible  vapours 
will  be  converted  into  permanent  gas.  Moreover,  whereas  there  is  no  limit  of  tem- 
perature beyond  which  it  might  be  inadvisable  to  heat  the  solid  residue,  the  same 
does  not  apply  to  the  primary  products,  as  too  great  exposure  t'o  intense  heat  has 
detrimental  results  in  their  case.  In  the  gas  retort  this  secondary  reaction  is  occa- 
sioned by  the  passage  of  the  pyoducts  through  the  heated  coke  mass  and  during 
their  travel  to  the  exit  of  the  retort  in  contact  with  the  heated  walls  of  the  vessel. 
Accordingly,  the  extent  to  which  the  primary  products  undergo  decomposition 
depends  partly  upon  the  limits  to  which  the  retort  is  heated,  but  in  greater  degree 
upon  the  manner  in  which  the  volatile  products  leave  the  retort  and  upon  the  time 


267 


spent  in  contact   with  the  hot  surfaces.       Degradation,  then,  may  be  assigned  to 
the  following  three  causes  : — 

(a)  The  temperature  to  which  the  products  are  submitted. 
(6)  The  nature  of  the  solid  surfaces  to  which  they  are  exposed, 
(c)  The  length  of  contact  time  with  these  surfaces. 

When  the  decomposition  is  such  as  to  be  beyond  the  economical  limit,  "  over- 
cracking  "  of  the  gases  and  vapours  is  said  to  occur,  It  will  be  seen  that  heat  may 
be  encountered  by  the  products  in  two  distinct  ways — namely,  by  contact  with  the 
heated  coke  and  retort  walls  and  by  direct  radiation  from  the  heated  surfaces.  Some 
years  ago  Young  pointed  out  that  the  action  of  these  two  forms  of  heat  is  distinct ; 
that  whereas  contact  with  the  hot  surfaces  appears  to  act  with  more  or  less  equal 
effect  on  all  substances,  the  radiant  heat  tends  to  have  a  selective  action,  and  most 
readily  attacks  those  molecules  which  absorb  heat  the  more  easily.  In  the  light 
of  recent  research,  however,  it  would  appear  that  this  conclusion  is  by  no  means 
established ;  the  most  severe  effects  seem  to  occur  during  the  passage  of  the  pro- 
ducts through  the  layers  of  red-hot  coke.  Chiefly,  it  is  found  that  the  heavy  hydro- 
carbons, particularly  the  olefmes,  the  acetylenes  and  the  lower  members  of  the 
paraffin  series,  are  most  prone  to  these  influences,  whilst  the  more  stable  methane 
is  only  affected  by  drastic  conditions.  The  small  proportion  of  rich  gas  present 
in  the  primary  products  consists  largely  of  ethane  and  its  homologues,  ethylene 
and  acetylene,  and  Colman  states  that  the  condensible  compounds  are  relatively 
rich  in  hydrogen,  and  belong  to  those  series  in  which  the  carbon  atoms  are  united 
in  open  chains.  If,  however,  they  are  present  in  closed  chains,  they  are  combined 
with  much  more  hydrogen  than  is  the  case  with  the  aromatic  hydrocarbons,  and 
are  probably  akin  to  the  naphthenes  and  similar  compounds.  In  their  passage 
through  the  coke  the  primary  gases  ethane,  ethylene,  acetylene,  and  methane  all 
tend  to  undergo  decomposition,  whilst  the  condensible  products  become  partly 
gasified  and  altered  in  character  to  some  extent.  Accordingly,  whilst  a  greater 
yield  of  permanent  gas  is  obtained  at  higher  temperatures,  considerable  deteriora- 
tion in  quality  follows  the  breaking  down  of  the  richer  constituents  into  less  valuable 
products. 

The  comparative  value  of  the  various  constituents  so  far  as  the  illuminating 
and  calorific  powers  of  the  ultimate  gas  are  concerned  is  emphasized  in  the  following 
table  : — 


Calorific  power  (gross). 

Candle-power. 

Benzene  . 

3,700  B.Th.U.  per  cubic  foot 

165 

candles  per  foot 

Ethane     

1,870 

,        , 

7 

>»            » 

Ethylene       

1,600 

,        , 

10 

»            » 

Methane  

1,020 

1 

Carbon  monoxide    

340 

nil 

Hydrogen      

325 

i 

' 

nil 

•268  MODERN   GASWORKS   PRACTICE 

With  regard  to  candle-power  the  effect  of  methane  is  questionable.  When 
'burned  by  itself  it  appears  to  show  but  poor  light-giving  properties,  but  when  present 
in  an  admixture  such  as  coal  gas  it  undoubtedly  accounts  for  an  increase  in  illumin- 
ating power  out  of  proportion  to  that  shown  in  the  above  table.  Whatever  its 
effect  as  an  illuminant,  however,  methane — owing  to  its  high  calorific  value — is 
one  of  the  most  desirable  constituents  of  modern  gas,  and  as  calorific  standards  of 
quality  gradually  supplant  the  now  obsolete  candle-power  test,  methane  will  increase 
in  importance.  Fortunately,  this  hydrocarbon  is  the  most  stable  of  those  present, 
and  consequently  suffers  to  a  comparatively  slight  extent  from  the  degrading  influ- 
ences in  the  retort. 

One  of  the  first  investigators  to  turn  his  attention  to  the  decomposition  of  gases 
was  Berthelot,  who,  in  1863,  carried  out  a  number  of  experiments  with  the  hydro- 
carbons. Previous  to  Berthelot's  work  it  had  been  shown  by  other  research  that 
the  ultimate  resolution  of  a  hydrocarbon  into  its  elements,  hydrogen  and  carbon, 
•  can  in  no  way  be  regarded  as  the  immediate  result  of  a  single  change,  but  that  gradual 
breaking  down  into  molecules  containing  a  smaller  number  of  atoms  takes  place. 
'  Thus  ethylene  (C2H4)  was  considered  to  be  resolved  into  free  carbon  and  methane,  and 
so  on. 

(a)  Ethylene,  C2H4  =  C  +  CH4. 

(6)  Ethane,  C2H6  =  C2H4  (ethylene)  +  H2. 

'  The  four  hydrocarbons  of  chief  interest  to  the  gas  engineer  are  the  primary  product 
ethane  (which  wholly  disappears  at  present-day  temperatures),  ethylene,  acetylene 
and  methane.  Berthelot,  as  a  result  of  his  studies,  was  of  the  opinion  that  these 
hydrocarbons  underwent  decomposition  in  the  following  manner  : — 

(a)  Ethane,  either  (1)  C2H6  =  C2H4  (ethylene)  +  H2, 

or  (2)  2C2H6  =  2CH4  (methane)  +  C2H2  (acetylene)  +  H2. 
(6)  Ethylene,  either  (1)  C2H4  =  C2H2  (acetylene)  +  H2, 

or  (2)  2C2H4  =  C2H6  (ethane)  +  C2H2  (acetylene). 

(c)  Acetylene.     This  he   concluded  was  never  resolved  into  its  elements,  but 
was  capable  of  undergoing  polymerization  or  condensation  into  benzene  at  high 
temperatures.     Thus  3C2H2  =  C6H6. 

(d)  Methane,  either  (1)  2CH4  =  C2H2  (acetylene)  +  3H2, 

or  (2)  2CH4  =  C2H6  (ethane)  +  H2. 

In  1894,  Lewes,  in  a  number  of  experiments  on  the  hydrocarbons,  of  which 
he  chiefly  studied  ethylene,  concluded  that  this  compound  is  primarily  decomposed 
into  equal  volumes  of  methane  and  acetylene  on  the  following  lines  : — 3C2H4  = 
2CH4  +  2C2H2.  With  regard  to  methane  he  agrees  with  Berthelot  that  this  is 
transformed  into  hydrogen  and  acetylene,  but  that  the  acetylene  subsequently 
polymerizes  or  is  resolved  into  its  elements  hydrogen  and  carbon.  All  are  agreed 
as  to  the  marked  stability  of  methane.  But  that  degradation  of  this  constituent 
does  take  place  at  higher  temperatures  and  under  certain  conditions  is  shown  by 


THE   CARBONIZATION   OF   COAL  260- 

the  manner  in  which  the  quantity  has  decreased  in  modern  coal  gas.  Lewes  states 
that  for  the  methane  to  fall  below  30  per  cent,  in  a  coal  gas  made  from  a  good  coal 
indicates  degradation  of  the  products  by  overheating,  and,  although  decomposition 
to  a  certain  extent  is  essential,  it  may  be  said  that  the  economical  limit  is  reached 
when  the  methane  has  been  reduced  to  about  30  per  cent. 

The  tendency  of  hydrocarbons  to  dissociate  is  well  illustrated  by  consideration 
of  their  structural  formulae  and  the  arrangement  of  the  carbon  affinities.  Thus, 
we  get — 

H        H  H        H 

II  II 

H  — C  — C  — H        H  —  C  — C  —  H        H  — C--C  — H 

i     I 

H        H- 

Ethane  (C2H6)  Ethylene  (C2H4)  Acetylene  (C2H2) 

In  each  case  it  will  be  seen  that  the  carbon  atoms  are  not  wholly  saturated1 
with  hydrogen,  and  in  order  that  each  affinity  may  fulfil  its  properties  of  attraction 
the  carbon  atoms  are  indicated  as  attracting  one  another.  A  bond  of  this  nature 
invariably  gives  rise  to  a  s»tate  of  instability,  so  that  the  molecule  at  this  point  tends- 
to  sever,  and  to  recombine  into  two  molecules  with  the  addition  of  hydrogen.  In 
the  case  of  ethylene  and  acetylene  this  tendency  becomes  still  more  marked,  as  a 
double  and  treble  bond  exists  between  the  carbon  atoms.  The  force  of  attraction 
between  the  atoms  virtually  acts  along  a  straight  line,  but  in  the  case  of  these  two 
compounds  it  may  be  looked  upon  as  being  bent  from  its  proper  path  and  curved 
round  so  as  to  unite  with  the  other  carbon  atom.  Hence  a  condition  of  strain  is- 
set  up  in  the  bond,  which  on  but  slight  provocation  straightens  out  and  takes  up 
another  hydrogen  atom.  Where  double  or  treble  bonds  exist  they  may  be 
taken  as  an  indication  of  instability  ;  and  the  greater  the  number  of  bonds  uniting 
the  carbon  atoms  the  greater  will  be  the  tendency  to  decompose.  Bone  supports 
this  theory  by  showing  that  acetylene  tends  to  break  down  across  the  triple  bond,, 
yielding  free  carbon  and  hydrogen,  whilst  if  other  hydrogen  is  taken  up  methane 
will  be  formed. 

Of  the  light-giving  hydrocarbons  in  coal  gas,  benzene  (which  is  present  to  the 
extent  of  about  0-75  per  cent.)  is  one  of  the  most  important.  Its  presence  has  been 
accounted  for  in  various  ways,  but  there  is  little  doubt  that  it  is  a  high  temperature 
degradation  product.  This  is  amply  shown  by  the  fact  that  whereas  modern  gas 
and  tar  emanating  from  heavy  coal  charges  are  of  a  distinctly  paraffinoid  nature,  the 
hydrocarbons  from  the  lighter  charges, which  afford  ample  opportunity  for  "over 
cracking,"  contain  a  greater  proportion  of  benzene  derivatives.  Many  investigators 
have  sought  to  prove  that  benzene  is  the  direct  result  of  the  polymerization  of 
acetylene.  Thus  three  molecules  of  acetylene  (united  in  open  chains)  undergo- 
rearrangement  to  yield  the  closed  benzene  formation  : — 


270  MODERN   GASWORKS   PRACTICE 

H 


/ 
(1)     H  —  C=C  —  H  //  \ 

H  —  CX        C  —  H 

•+(2)     H  —  C  =  C  —  H       gives 


+  (3)     H— C=C— H  C^N   X°     ~H 

C 

I 
H 

There  is  little  doubt  that  such  a  reaction  takes  place  to  a  certain  extent,  although, 
in  the  main,  it  seems  probable  that  the  benzene  results  at  moderate  temperatures 
from  the  paraffin  derivatives.  Bone  has  found  that  at  low  temperatures  acetylene 
exhibits  a  strong  tendency  to  polymerize,  forming  benzene,  etc.,  so  that  when  acety- 
lene is  the  principal  primary  product  in  the  decomposition  of  another  hydrocarbon 
(for  example,  ethylene)  there  is  always  a  marked  secondary  formation  of  benzene 
and  other  aromatic  hydrocarbons.  This  tendency  towards  polymerization  reaches 
its  maximum  between  1,000°  and  1,300°  Fahr.  and  practically  ceases  to  exist  above 
1,800°  Fahr. 

With  regard  to  the  actual  method  of  decomposition  of  the  hydrocarbons  the 
work  of  Bone  (1908)  may  be  looked  upon  as  classical.  This  investigator  has  pro- 
pounded entirely  new  theories,  based  on  the  fact  that  carbonaceous  residues,  such 
as  CH  and  CH2,  are  capable  of  an  extremely  fugitive  existence.  With  the  exception 
of  methane,  however,  he  is  of  the  opinion  that  the  mode  of  decomposition  of  any 
particular  hydrocarbon  cannot  be  expressed  by  means  of  a  single  chemical  equation. 
'The  degradation  of  methane  is,  in  the  main,  a  direct  disunion  into  carbon  and  hydro- 
gen— CH4  =  C  -f-  2H2.  The  free  carbon  deposited  from  this  reaction  is  of  a  hard 
and  lustrous  type,  being  wholly  different  from  that  resulting  from  the  decomposition 
of  the  other  hydrocarbons.  So  far  as  ethane  and  ethylene  are  concerned,  the  effect 
of  high  temperatures  is  to  cause  a  dissolution  of  the  bonds  uniting  the  carbon  atoms, 
thus  giving  rise  to  the  residues  =:  CH  and  ^H  CH2.  Bone  states  that  these  residues 
may  subsequently — 

(1)  Meet  with  other  similar  residues  and  form  H2C  ZZCH2  and  HC  =  CH 

(2)  Break  down  directly  into  carbon  and  hydrogen. 

(3)  Are  directly  hydrogenized  into  methane. 

These  three  reactions  may  occur  simultaneously,  depending  upon  the  temperature, 
pressure,  and  amount  of  hydrogen  prevailing.  In  the  case  of  ethane,  Bone  represents 
the  changes  in  the  following  way : — 

^H        H  ,-, 

Ethane  =    H  —  C  ~TT  C  —  H 

I    !!    I 
H/VH 


THE   CARBONIZATION   OF   COAL  271 

The  bond  between  the  carbon  atoms  tends  to  break  away,  whilst  two  hydrogen 
atoms  also  escape,  thus  decomposing  the  molecule  into  three  distinct  portions, 
namely  :— CH2,  CH2,  and  H2.     Ethane  then  has  yielded  [2(CH2)  +  H2]  which  on 
recombination  may  become  either — 
(1)  C2H4  (ethylene)  +  H2, 

or  (2)  20  +  2H2  +  H2, 
and  by  hydrogenation,  i.e.  +  H2,  we  get — 
(3)  2CH4  (methane). 

In  the  same  way  ethylene  has  a  tendency  to  split  up  across  the  double  carbon 
bond  into  the  following  residues  : — 

\  H        H 


Ethylene  =  H  —  C  Zl'C  —  H  =  [2(CH)  +  H,]. 

!  I 
These  then  reunite  to  yield — 

(1)  C2H2  (acetylene)  -f  H2  (hydrogen), 
or  (2)  20  +  H2  +  H,, 

or  (3)  by  hydrogenation  (i.e.  +  2H2),  =  2CH4  (methane). 
With  regard  to  acetylene,  the  change  may  take  place  either  by  polymerization, 
as  already  mentioned,  or  by  dissolution  into  residues.     In  the  latter  case  a  weakness 
develops  across  the  triple  bond  between  the  carbon  atoms  :— 

Acetylene  =  H  —  C  ±E  C  —  H  =  2  (  =  OH). 

«  t  \ 

i    \ 

The  OH  residues  then  give — 

(a)  20  +  H,, 
or  (6)  by  hydrogenation  (i.e.  +  3H2)  —  2CH4  (methane). 

There  is  little  doubt  that  in  addition  to  degradation  a  certain  amount  of  syn- 
thesis takes  place  at  definite  temperatures  in  the  retort.  The  increase  in  the  quantity 
of  methane  at  higher  temperatures  is  in  all  probability  due  to  this  cause.  Burgess 
and  Wheeler,  in  their  well-known  work,  state  that  evolution  of  hydrocarbons  of 
the  paraffin  series  ceases  almost  entirely  at  temperatures  above  1,290°  Fahr.  ;  but 
at  the  same  time  there  are  certain  indications  of  an  increase  in  the  methane  above 
this  point.  Pring  and  Fairlie,  in  a  contribution  to  the  proceedings  of  the  Chemical 
Society,  state  that  results  of  their  experiments  show  that  at  temperatures  between 
1,300°  and  1,350°  Fahr.  acetylene  reacts  with  hydrogen  to  give  methane  and  ethylene. 
At  a  temperature  of  2,200°  Fahr.  carbon  was  found  to  combine  with  hydrogen  to 
give  both  methane  and  ethylene,  the  rate  of  formation  of  the  methane  being  100 
times  that  of  the  ethylene.  A  certain  amount  of  acetylene  was  also  formed  at  this 
temperature,  but  the  quantity  was  too  small  to  be  measured. 

Some  of  the  most  enlightening  work  on  the  behaviour  of  the  hydrocarbons 
has  recently  been  carried  out  by  Oobb  and  Rollings,  at  Leeds  University.  In  this 
instance  a  small  portion  of  coal  was  distilled  in  a  boat  and  the  volatile  products 


272 


MODERN   GASWORKS   PRACTICE 


were  subjected  to  various  conditions.  In  the  first  case  they  were  removed  from  the 
heated  tube  with  the  utmost  rapidity  ;  secondly,  they  were  subjected  to  the  radiant 
heat  of  the  tube  ;  and,  thirdly,  they  were  collected  after  passage  through  a  heated 
coke  surface.  The  results  obtained  go  clearly  to  show  that  the  last-named  condition 
is  attended  by  the  most  severe  forms  of  degradation.  A  summary  of  these  results 
is  given  here,  and  Table  I  indicates  the  percentage  composition  of  the  gas  obtained 
under  the  different  conditions. 

TABLE  I 

PERCENTAGE  COMPOSITION  OF  NITROGEN-FREE  GAS 


Minimum 
heat  action. 

Radiant 
heat. 

Hot  coke 
surface. 

Unsaturated  hydrocarbons   .     '. 
Methane      

Per  cent. 
6-3 
33-1 

Per  cent. 
5-0 
30-9 

Per  cent. 
3-3 
27-3 

Hydrogen  

42-5 

46-6 

51-2 

Carbon  monoxide  

13-1 

14-3 

14-7 

Carbon  dioxide     .      .      .  ,    . 

4-3 

3-4 

3-2 

Oxygen       

0-7 

0-1 

0-5 

At  the  same  time  the  actual  volume  of  each  constituent  obtained  in  cubic  centi- 
metres per  gramme  of  coal  was  recorded.  In  Table  II  these  figures  have  been  reduced 
to  cubic  feet  per  ton — a  measurement  with  which  the  gas  engineer  is  more  familiar. 


TABLE    II 

YIELD  OF  NITROGEN-FREE  GAS 


Minimum 
heat. 

Radiant  heat. 

Hot  coke  surface. 

Expt.  I. 

Expt.  II. 

Expt.  I. 

Expt.  II. 

Unsaturated  hydrocarbons 
Methane  . 
Hydrogen      

538 
3,157 
4,197 
1,614 

525 
3,552 
5,346 
1,614 

563 
3,444 

5,238 
1,471 

287 
3,516 
6,315 
2,045 

472 

3,588 
6,708 
1,937 

Carbon  monoxide    .... 

Cubic  feet  per  ton 

9,506 

11,037 

10,716 

12,163 

12,705 

It  is  seen  that  the  result  of  subjecting  the  volatile  products  to  the  action  of 
radiant  heat  is  an  increase  of  about  14  per  cent,  in  "  make  "  per  ton,  whilst  by  pas- 
sage through  the  column  of  heated  coke  the  increase  amounts  to  30  per  cent.  That 
the  quality  of  the  gas  is  lowered  by  the  decomposition  which  has  resulted  from  the 
further  action  of  heat  is  shown  by  the  reduction  which  has  occurred  in  the  propor- 


THE   CARBONIZATION   OF   COAL 


273 


tion  of  heavy  hydrocarbons  present.  Hydrogen  has  increased  in  volume  by  50  per 
cent.,  whilst  methane  remains  moderately  steady,  showing  that  the  extra  hydrogen 
has  not  been  obtained  at  its  expense.  The  hydrogen  appears  to  be  chiefly  the 
product  of  the  decomposition  of  the  heavy  hydrocarbons  and  of  the  gasification 
of  a  portion  of  the  tar. 

Cobb  and  Rollings  also  conducted  experiments  on  the  decomposition  of 
the  various  hydrocarbons  in  the  presence  of  hydrogen  and  methane,  and,  there- 
fore, under  conditions  approximating  to  those  prevailing  in  a  retort.  A  mixture 
was  taken  consisting  of  equal  parts  of  hydrogen  and  methane  to  which  were  added 
small  percentages  of  the  hydrocarbons  to  be  tested.  Temperatures  of  1,470°  Fahr. 
and  2,000°  Fahr.  were  selected  for  the  study  of  decomposition,  and  only  experi- 
ments in  which  the  gases  were  passed  through  a  tube  packed  with  coke  have  so  far 
been  recorded.  With  regard  to  methane  it  was  found  that  at  1,470°  Fahr.  only  about 
2  per  cent,  was  decomposed  in  one  minute,  whereas  at  2,000°  Fahr.  degradation  is 
very  rapid.  In  the  latter  case,  however,  there  was  an  increase  in  volume  of  about 
44  per  cent.  ;  but  a  considerable  loss  of  calorific  value  was  noticed  owing  to  the 
carbon  of  the  decomposed  methane  being  deposited  in  the  solid  state.  The  results 
of  the  two  experiments  are  shown  below. 

METHANE 


At  1,470°  Fahr. 

At  2,000°  Fahr. 

Gas  before 
Gas  afterward 

(Methane    .      .      .      i      .  '   . 
(Hydrogen.      .      .      .      .      . 
(Methane    .      .      . 
I  Hvdrosren. 

50-9  per  cent. 
49-1 
49-5        „ 
50-5         „ 

50-9  per  cent. 
49-1 
6-6 
93-4 

Percentage  of 

methane  decomposed  .... 

2.0 
o            » 

87 

So  far  as  ethane  is  concerned  it  was  found  that  the  chief  products  of  its  decom- 
position are  ethylene  and  methane.  At  1,470°  Fahr.  the  following  results  were 
noted  after  heating  for  forty-six  seconds  : — 

ETHANE,  at  1,470°  Fahr. 


Composition  of  gas. 

Before. 

After. 

Ethane  

4  -2  per  cent 

Methane      

47-5 

48-9 

Hydrogen    

48-3 

48-9 

Ethylene     

nil 

1-3 

Acetylene    . 

nil 

Trace 

In  this  case  the  percentage  of  ethane  decomposed  amounts  to  79,  but  at  a  tem- 
perature of  2,000°  Fahr.  the  figure  rose  to  88  per  cent. 

Ethylene  was  found  to  show  rather  more  stable  properties  than  ethane,  the 


«274  MODERN   GASWORKS   PRACTICE 

quantity  decomposed  at  1,470°  Fahr.  being  62  per  cent,  after  heating  for  forty-five 
seconds,  and  at  2,000°  Fahr.  no  trace  of  the  product  remained.  The  decomposition 
products  consisted  largely  of  hydrogen  and  methane,  with  a  very  small  proportion 
of  acetylene  at  the  lower  temperature. 

The  experiments  with  benzene  are  of  particular  interest  in  that  they  indicate 
the  stable  nature  of  this  product  at  low  and  moderate  temperatures  and  its  com- 
plete instability  at  higher  temperatures.  At  1,470°  Fahr.  the  decomposition  was 
negligible,  but  at  2,000°  Fahr.  a  very  different  result  was  obtained. 

BENZENE,  at  2,000°  Fahr.,  heated  for  forty-two  seconds. 


Composition  of  gas. 

Before. 

After. 

Benzene      . 
Methane      
Hydrogen                           

5-0  per  cent. 

47-8 

47-2 

nil 
11-1  per  cent. 
88-4            „ 

Ethylene     

nil 

nil 

Acetylene    

nil 

Trace 

THE  PROBLEM   OF   INCREASED   YIELDS 

Whereas  a  decade  ago  the  gas  engineer  obtained  little  more  than  10,000  cubic 
feet  of  gas  from  every  ton  of  coal  carbonized,  to-day  he  is  enabled,  with  the  more 
efficient  apparatus  at  his  disposal,  to  swell  this  yield  to  as  much  as  14,000 
cubic  feet.  This,  however,  would  not  have  been  possible  but  for  the  fact  that 
the  changing  applications  of  gas  have  rendered  the  illuminating  standard  ob- 
solescent, with  the  result  that  penal  restrictions  in  this  direction  have  been 
lowered.  It  is  improbable  that  finality  in  regard  to  gas  "  makes  "  has  yet  been 
reached.  Experiments  conducted  by  Mr.  Thos.  Goulden  appear  to  indicate  that 
even  higher  results  may  be  expected  in  the  future.  In  tests  with  a  Durham  coal 
he  obtained  no  less  than  15,840  cubic  feet  of  gas  having  the  remarkably  high  calorific 
power  of  530  B.Th.U.  gross.  In  this  case  the  illuminating  power  had  dropped  to 
twelve  candles,  but  the  most  noticeable  feature  was  the  gradual  advance  of  the  heat 
units  obtained  in  the  gas  as  the  volume  increased.  With  the  highest  yield  this 
increase  amounted  to  no  less  than  15  per  cent,  as  compared  with  the  units  obtained 
when  the  "  make  "  was  12,000  cubic  feet  per  ton.  Without  enrichment  a  gas  of 
twelve  candle-power  would,  of  course,  be  unsuited  for  distribution  in  many  areas 
at  the  present  time,  but  with  the  advent  of  statutory  requirements  based  on  calorific 
power  alone,  it  is  possible  that  large  yields  such  as  this  may  become  the  fashion. 

The  chief  points  of  interest  are  the  means  which  have  been  employed  in  increasing 
the  yield  of  permanent  gas  by  so  much  as  40  per  cent.  Primarily,  the  introduction 
of  the  modern  form  of  regenerative  setting  composed  of  material  having  greatly 
improved  refractory  qualities  has  rendered  the  first  essential — the  employment  of 
high  distillation  temperatures — possible.  The  prolonged  heating  of  the  solid  residue 
at  temperatures  of  about  2,000°  Fahr.  is  followed  by  the  evolution  of  almost  the 


THE   CARBONIZATION   OF   COAL  275 

last  traces  of  volatile  matter,  with  the  result  that  the  constituents  of  present-day 
coke  are  almost  wholly  of  a  "  fixed  "  nature.  It  must  be  realized,  however,  that 
the  procurement  of  high  makes  of  gas  does  not  in  any  way  depend  solely  upon  the 
efficient  burning-off  of  the  charge,  but  is  due  to  a  combination  of  small  influences, 
each  of  which  requires  expert  and  detailed  supervision.  On  the  average  gasworks 
there  are  many  insignificant  items,  probably  unnoticed  in  the  general  way,  which 
may  account  for  some  slight  disorganization  of  working,  and — as  the  engineer  with 
record  "  makes  "  to  his  credit  knows  full  well — it  is  the  suppression  of  these  and 
the  maintenance  of  the  whole  machine  up  to  concert  pitch  which  tells  its  tale  in  the 
end.  In  addition  to  the  higher  heats  of  distillation  now  in  use,  the  increased  volume 
of  gas  may  be  ascribed  largely  to  the  following  : — 

(a)  More  complete  gasification  of  tarry  vapours,  so  that  otherwise  condensible 
products  yield  permanent  gas. 

(6)  Increase  of  volume  obtained  by  over-cracking  the  primary  gas  within  the 
economical  limit. 

(c)  The  use  of  light  seals,  or  no  seals,  in  the  "  hydraulic  "  main,  and  the  strict 
avoidance  of  tar  seals. 

(d)  The  employment  in  the    hydraulic    main    of    a  vacuum  slightly  greater 
than  the  intensity  of  seal  on  the  dip-pipe. 

(e)  The  use  of  heavy  charges  of  coal  in  the  retort. 

(/)  Steaming  the  coal  charge,  as  may  be  carried  out  in  certain  types  of  vertical 
retorts. 

(g)  The  employment  of  prolonged  charges  in  preference  to  those  of  short 
duration  as  used  some  few  years  ago. 

(h)  The  discreet  admission  of  air  for  the  improvement  of  the  process  of 
purification,  etc. 

(i)  Over-exhausting. 

Nothing  has  been  said  with  regard  to  the  quality  of  coal  made  use  of,  this  having 
some  considerable  influence  on  the  final  results.  It  is,  however,  a  factor  over  which 
the  average  gas  engineer  has  little  control,  it  usually  being  necessary  (on  the  grounds 
of  economy)  to  take  the  coal  from  the  nearest  colliery. 

It  will  be  seen  that  the  increased  volume  is  composed  chiefly  of — 

(a)  Hydrogen,  from  the  coke  residue,  from  degradation,  and  from  the  gasified 
tarry  vapours. 

(6)  Methane,  from  the  gasified  tarry  vapours  and  from  degradation  of  heavy 
hydrocarbons,  also  to  some  extent  from  synthetic  sources  at  the  higher  temperatures, 
A  portion  of  this  methane  is  eventually  decomposed,  so  that  in  the  final  gas  it  shows 
some  deficiency  compared  with  lower  yields  of  gas. 

(c)  Nitrogen,  from  in-travel  of  the  furnace  gases,  from  the  residual  coke,  which 
chiefly  evolves  this  gas  in  the  final  stages,  and  from  the  atmosphere. 

(d)  Carbon  monoxide,  from  the  formation  of  water  gas  (particularly  if  "  steam- 
ing "  is  practised),  and  from  the  reduction  at  high  temperatures  of  carbon  dioxide. 

(e)  Carbon  dioxide,  from  the  in-travel  of  furnace  gases. 
(/)  Oxygen,  from  the  atmosphere. 


276 


MODERN   GASWORKS   PRACTICE 


The  effect  of  one  important  influence — that  of  over-exhausting — is  admirably 
illustrated  in  the  following  table,  in  which  the  make  in  neither  case  is  particularly 
high,  but  which  gives  an  excellent  indication  of  the  manner  in  which  the  additional 
800  cubic  feet  of  gas  per  ton  is  accounted  for  : — 


Level-gauge  in  retort. 

Over  -exhausting. 

Difference  . 

Cubic  feet  per  ton 

Cubic  feet  per  ton 

of  coal. 

of  coal. 

Hydrogen  

5,676 

5,709 

+     33 

Methane     . 

3,780 

3,494 

-  286 

Carbon  monoxide      .... 

1,164 

1,254 

+     90 

Carbon  dioxide     

264 

346 

+     82 

Heavy  hydrocarbons       .      .'    . 

408 

422 

+      14 

Oxygen  

60 

90 

+     30 

Nitrogen     

648 

1,485 

+   837 

Total  

12,000  cubic  feet 

12,800  cubic  feet 

+   800 

Candle-power  

18 

15 

Calorific  power     .      .      .      .  '  . 

575  B.Th.U. 

559  B.Th.U. 

The  table  is  compiled  from  percentage  composition  figures  obtained  by  Dr. 
Davidson  in  distilling  a  standard  second  class  Midland  coal.     The  most  noticeable 
results  of  the  over-exhausting  are  a  marked  deficiency  in  the  valuable  heavy  hydro- 
carbons and  methane,  whilst  nitrogen  has  increased  by  130  per  cent. 

The  question  as  to  the  increase  of  volume  of  permanent  gas  obtained  by  over- 
cracking  in  the  free  space  is  a  vexed  one,  and  some  authorities  point  out  that  the 
yield  is  swelled  to  only  a  meagre  extent  in  this  way.      If  we  consider  any  of  the 
degradation  reactions,  however,  it  is  possible  to  show  by  means  of  Avogadro's  law 
that  some   increase  of  volume  does  take  place.     For  instance,   if  the  reaction 
CH4  =  C  +  2H2  is  taken  as  an  example  it  is  seen  that  one  molecule  of  methane  gives 
rise  to  two  molecules  of  hydrogen.     In  other  words,  a  cubic  foot  of  methane  yields 
on  degradation  double  its  volume  of  hydrogen  ;  that  is,  an  increase  of  100  per  cent, 
in  permanent  gas.     Similarly,  ethylene  (C2H4)  n  ay  decompose  into  acetylene  (C2H2) 
and  hydrogen  (H2).     Thus  one  molecule  has  yielded  two  molecules  of  gas  ;  again  an 
increase  in  volume  of  100  per  cent.     The  extent  of  such  decomposition,  however,  is 
relatively  small  in  comparison  with  the  total  volume  of  gas  present,  and  Lewes  has 
shown  that  in  the  long  run  intentional  over  cracking  in  the  retort  will  probably 
account  for  only  an  additional  400  or  500  cubic  feet.     Lewes'  experiment  on  the 
effect  of  degradation  of  the  primary  products  is  of  extreme  interest.     First,  he 
obtained  a  semi-primary  gas  having  an  analysis  approximately  as  follows : — 
Hydrogen       .         ;         .         .         .         .         .         .         .         .     27-5  per  cent. 

Saturated  hydrocarbons — 1,  Methane        .          .          .          .          .48-0         „ 

„  „  2,  Higher  members  ....     10-1         „ 

Unsaturated  hydrocarbons       .   '    ' .  .          .          .          .       3-0         „ 

Carbon  monoxide  .........       7-3         „ 

Carbon  dioxide       .         .         .         .         .         .         .•         .         .       2-5         „ 

Nitrogen        .         .         .         .         .         .         ...         .1-6        ,, 


THE   CARBONIZATION   OF   COAL  277 

This  gas  was  then  passed  through  a  tube  containing  broken  porcelain,  and 
heated  to  1,830°  Fahr.,  when  an  increase  of  volume  of  11  per  cent,  resulted,  the 
composition  then  being  as  follows  :  — 

Hydrogen       ..........     52-3  per  cent. 

Methane         .          .          .          .          .          .          .          .          .          •     34-0 

Unsaturated  hydrocarbons       .          .          .          .          .          .          .       2-5 

Carbon  monoxide  .          .          .          .          .          .          .          .          .       8-8 

Carbon  dioxide       .          .          .  "       .          .          .          .          .          .1-0 

Nitrogen         .          .          .          .          .'        .          .          .          .          .       1-4 

The  original  volume  of  semi-primary  gas  obtained  amounted  to  4,500  cubic 
feet,  and  this  was  swelled  to  11,200  cubic  feet  by  the  second  treatment.  The  most 
interesting  feature  of  the  experiment,  however,  is  the  manner  in  which  the  increased 
volume  of  gas  is  obtained.  This  is  shown  as  follows  :  — 

Volume  composed  of  :  — 

Primary  gas        .          .          .          ,          .          .          .  .  .  4,500  cubic  feet. 

Increase  of  volume  due  to  degradation         .          .  .  .        495       „        „ 

Gas  expelled  from  low  temperature  coke  residue  .  .  .  5,000       „        „ 

Gas  due  to  gasification  of  -tar      .          .          .          .  .  .  1,205       „        „ 


Total  yield       11,200  cubic  feet  per  ton. 

With  regard  to  the  final  tar  as  yielded  by  Dessau  vertical  retorts,  Davidson 
has  shown  that  1  gallon  when  gasified  will  produce  68  cubic  feet  of  gas  having  a 
candle-power  of  17-35.  In  the  ordinary  way  the  yield  of  tar  from  coal  carbonized 
for  prolonged  periods  at  high  temperatures  varies  from  12  to  14  gallons  per  ton, 
whereas  with  a  gas  make  approaching  only  5,000  cubic  feet  per  ton  the  tar  recovered 
would  be  in  the  neighbourhood  of  20  to  22  gallons.  The  difference  between  these 
two  figures  represents  the  quantity  of  tar  which  under  modern  conditions  is  trans- 
formed into  permanent  gas  and  free  carbon.  The  character  of  the  tar  is,  moreover, 
considerably  affected.  When  the  gas  has  been  subjected  to  the  prolonged  influ- 
ence of  secondary  heat  a  tar  of  a  distinctly  benzenoid  character  results,  whilst  when 
the  decomposition  is  limited  —  as  with  modern  methods  —  the  tar  consists  largely 
of  derivatives  comprised  in  the  paraffin  series. 

The  problem  as  to  whether  it  is  more  profitable  to  aim  at  high  tar  yields  and 
medium  gas  makes  or  abnormal  gas  makes  and  low  tar  yields  is  one  upon  which 
many  and  varying  opinions  have  been  given.  It  is  of  more  than  passing  interest 
in  that  it  really  represents  the  distinction  between  the  results  obtained  with  hori- 
zontal and  continuous  vertical  retorts.  There  can  be  little  dispute  that  so  far  as 
gas  yields  are  concerned  the  horizontal  systems  worked  on  efficient  lines  can  more 
than  hold  their  own,  while  the  rival  system  presents  many  advantages  in  regard  to 
tar,  liquor,  sulphur  impurities,  and,  perhaps,  naphthalene.  The  claim  as  regards 
naphthalene  is  one  which  requires  a  little  qualification,  for  with  the  general  adoption 
of  the  heavy  charge  in  horizontal  retorts  naphthalene  and  stopped  ascension  pipes 
may  be  looked  upon  almost  as  things  of  the  past,  when  ordinary  precautions  are 
taken. 


278  MODERN   GASWORKS   PRACTICE 

The  primary  objection  to  intermittent  systems  of  carbonization  is  the  manner 
in  which  the  quality  of  gas  evolved  undergoes  deterioration  as  the  period  of  dis- 
tillation proceeds.  Thus  during  the  first  quarter  of  an  hour  there  is  a  burst  of  gas 
of  good  quality 'very  much  resembling  the  semi-primary  gas  given  in  the  table  on 
page  276.  Although  carried  out  some  years  ago,  the  experiments  of  L.  T.  Wright 
on  the  extent  of  deterioration  still  prove  most  instructive.  The  following  figures 
obtained  by  Wright  give  an  excellent  idea  of  this  effect : — 

COMPOSITION  or  GAS  AT  VARIOUS  PERIODS  OF  CHARGE 

Period  from  Commencement  (Approximate). 

10  minutes.  1J  hours.  3 J  hours.  5 i  hours. 

Hydrogen       .          ...          .          .     20-10     . .  38-08     . .  50-68     . .  67-12  per  cent. 

Methane         .          .          .    •      .          .          .     57-38     . .  44-03     . .  35-54     .  .  22-58 

Heavy  hydrocarbons       ....     10-62     . .  5-98     . .  3-04     . .       1-79 

Carbon  monoxide 6-19     . .  5-98     . .  6-21      . .       6-12 

Carbon  dioxide        .    -     ,         .          .          .       2-21     ..  2-09     ..  1-49     ..       1-50 

Sulphuretted  hydrogen   .          .          .          .       1-30     ..  1-42     ..  0-49     . .       0-11 

Nitrogen 2-20     ..  2-47     ..  2-55     ..       0-78 


100-00          100-00          100-00          100-00 

The  results  were,  of  course,  obtained  at  lower  temperatures  than  those  now 
prevailing,  and  under  old-fashioned  conditions  of  seal  and  vacuum,  so  that  at  the 
present  day  it  would  be  unlikely  that  the  nitrogen  content  would  remain  practically 
constant,  and  even  show  the  reduction  which  Wright  found  after  five  and  a  half 
hours.  In  fact,  in  connexion  with  the  heavy  twelve-hour  charge  the  author,  in 
recent  experiments,  finds  that  with  a  |-inch  seal  and  l|-inch  "draw"  the 
composition  approximates  to  the  following  : — 

After  6  hours.  After   12  hours. 

Hydrogen     .          .  .  .  •          .     45-2  per  cent.  65-8  per  cent. 

Methane        .  .          .          .     22-9         „  1-4 

Heavy  hydrocarbons  .  ...  .       4-1         „  nil 

Carbon  monoxide.  .  .6-3         ,,  15-2         „ 

Carbon  dioxide     .  .  ....       2-6         „  0-6 

Nitrogen    •  i'  .      .  .  .     18-0        „  16-6 

So  far  as  nitrogen  only  is  concerned  (determined  by  the  direct  method)  the 
following  figures  are  given  as  typical  of  those  obtained  under  the  rather  severe  and 
abnormal  conditions  quoted  above  : — 

After  1  hour         ...         .         •        ••         •          •     11-6  Per  cent-  °*  nitrogen. 

„     2  hours       . 14-8  „  ,, 

3  ....     16-4 


4 
5 
6 
7 
8 
9 

10 
11 
12 


16-7 
17-5 
18-5 
19-7 
20-1 
20-2 
15-9 
15-2 
15-2 


THE   CARBONIZATION   OF   COAL 


279 


In  the  modern  form  of  coke  oven  it  is  customary  to  carbonize  the  heavy  charges, 
amounting  in  some  cases  to  as  much  as  10  tons,  for  periods  of  twenty- four  hours,  or 
even  longer.  Under  such  conditions  the  deterioration  becomes  somewhat  excessive 
towards  the  end  of  the  period,  as  is  shown  by  the  following  results,  obtained  by 
Simmersbach  for  a  twenty- nine  hour  charge. 


Hour  of  car- 
bonization. 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

15. 

17 

19 

21 

23 

25- 

27 

Gas  analysis. 

C08 
C6H6 

3-3 
1-8 

3-0 
1-5 

2-3 
1-1 

Sr-6 

1-1 

2-2 
1-0 

2-0 
0-8 

1-4 
0-6 

1-9 
0-5 

2-3 
0-35 

1-3 
0-35 

1-5 
0-35 

2-0 
0-3 

1-9 
0-25 

1-8 
0-1 

1-1 

1-05 

0-8 

0-7 

1-0' 

C2H4 

4-0 

3-5 

3-1 

3-2 

2-S 

?*5 

2-5 

2-0 

1-75 

2-05 

1-85 

1-8 

1-8 

1-9 

1-2 

1-0 

0-6 

0-3 

0-3: 

02 

1-05 

0-8 

0-6 

0-6 

0-5 

0-5 

0-2 

0-2 

0-2 

0-1 

0-2 

0-2 

0-15 

0-25 

0-1E 

0-05 

0-05 

0-1 

0-3: 

CO 

0-9 

1-9 

2-9 

2-8 

3-0 

3-95 

3-4 

3-1 

2-8 

S-8 

4-15 

4-1 

3-9 

4-15 

4-7 

4-0 

3-8 

4-9 

5-8 

CH4 

36-65 

36-1 

34-5 

34-5 

33-6 

32-4 

35-65 

33-45 

31-2 

32-4 

33-4 

32-45 

33-2 

30-6 

26-1 

21-15 

1K-95 

If  -2 

4-7 

H2 

42-5 

44-6. 

48-8 

47-8 

50-1 

50-75 

53-65 

50-55 

47-1 

51-5 

50-65 

49-75 

53-4 

51-6 

55-75 

38-95 

61-9 

37-0 

70-0 

N2 

10-0 

8-6 

6-7 

7-5 

6-8 

7-1 

3-6 

8-3 

14-3 

9-5 

7-9 

0-4 

5-4 

8-6 

11-0 

13-8 

13-9 

14-8 

17-» 

The  coke  yielded  contained  2-56  per  cent,  of  volatile  matter  and  88-53  per  cent, 
of  carbon.  The  nitrogen,  it  will  be  noticed,  is  at  a  minimum  (3'6  per  cent.)  at  the 
eighth  hour,  but  is  five  times  this  amount  at  the  twenty-seventh. 


Less  than  a  decade  ago  it  was  the  recognized  custom  to  employ  light  charges 
in  the  retort,  and  to  work  these  off  in  short  periods  of  carbonization.  Six  hours 
was  looked  upon  as  a  convenient  period,  so  that  the  retort  could  be  filled  four  times 
during  the  twenty-four  hours.  When  such  systems  are  adopted  the  coal  lies  in  a 
thin  layer  upon  the  floor  of  the  retort,  thereby  leaving  a  large  crown  space  unoccu- 
pied. By  prolonging  the  period  to  either  eight  or  twelve  hours  the  labour  entailed 
is  curtailed  by  one-third  or  a  half,  and  many  further  advantages  accrue.  With  the 
six-hour  charge  the  weight  of  coal  distilled  in  a  "  through  "retort  of  average  cross- 
section  was  usually  G  cwts.  ;  and  it  may  be  taken  as  a  rough  rule  that  the  number 
of  cwts.  shall  be  equivalent  to  the  period  of  carbonization  in  hours. 

Thus,  a  6-hour  charge  consists  of     6  cwts. 

an  8-hour      ,,  ,,         ,,8     ,,. 

and  a  12-hour       ,,  ,,         ,,  12     ,, 

In  each  case  it  will  be  seen  that  the  weight  of  coal  employed  in  twenty-four 
hours  is  approximately  the  same  ;  but  whereas  in  the  six-hour  charge  it  has. 
to  be  handled  on  four  distinct  occasions,  with  the  twelve-hour  charge  only  two 
handlings  are  necessary.  The  primary  objection  to  the  six-hour  charge  is,  however, 
the  excessive  degradation  and  decomposition  which  takes  place  in  the  greater  free- 
space  above  the  coal.  Owing  to  the  tendency  of  the  gas  to  linger  in  the  retort,  and 
to  its  slow  passage  there  though,  in  contact  with  incandescent  surfaces  of  carbon,  the 
destructive  influences  are  afforded  exceptional  facilities  for  working  their  evil.  It 


280  MODERN   GASWORKS   PRACTICE 

must  be  remembered,  moreover,  that  although  decomposition  by  heat  occurs  in  what 
may  seem  a  minute  space  of  time,  in  the  ordinary  way  the  thermal  degradation  of 
"the  hydrocarbons  takes  place  very  slowly  in  comparison  with  the  rate  at  which  many 
•other  chemical  reactions  occur.  Thus  an  increased  time  of  exposure  tells  heavily 
in  this  direction.  As  the  bulk  of  gases  travel  along  the  free  space  to  the  outlet  pipe, 
portions  of  them  will  be  in  contact  with  the  sides  of  the  retort,  etc.,  where  their 
temperature  quickly  rises  to  that  of  the  surfaces,  and  it  is  here  probably  that  the 
most  intense  degradation  occurs.  The  gases  towards  the  middle  of  the  bulk,  how- 
ever, absorb  the  radiant  heat  traversing  the  space,  and  as  the  more  complex  com- 
pounds have  a  greater  absorptive  capacity  than  the  simpler  bodies  for  radiant  heat, 
the  tendency  is  for  the  more  stable  gases,  such  as  methane,  to  remain  unharmed 
whilst  the  complex  vapours  are  split  up.  It  is  for  this  reason  that  the  condensible 
vapours  and  gaseous  hydrocarbons  are  of  a  distinctly  benzenoid  character  with  light 
charges.  Furthermore,  the  excessive  degradation  gives  rise  to  the  deposition  of 
free  carbon,  which,  in  turn,  causes  stopped  pipes  ;  and  naphthalene  makes  its  appear- 
ance in  undesirable  quantities.  The  naphthalene  formation  may  be  explained  by 
the  fact  that  when  subjected  to  excessive  heat  benzene  probably  polymerizes,  so 
that  the  following  compounds  containing  condensed  benzene  nuclei  are  formed  : — 

H  H  H  H  H 

I        I 

C          Cv 

W,_^N'  /•>  O  - LJ  H 

•*  V»  \*  \s 


Cv        C  C  — H          H— 

V  /    \ 
XC  C 


c 


c  c 


C 


H  H  H  H  H 

Naphthalene  Anthracene 

During  the  formation  of  such  compounds  hydrogen  is  evolved  in  some  quantity, 
and  accounts  for  the  high  percentage  of  this  gas  usually  found  in  the  resultant  gas 
from  light  charges.  With  regard  to  the  "  free  "  carbon  deposited,  it  is  interesting 
to  note  that  Colman  considers  that  with  still  higher  temperatures  and  with  increase 
of  time  the  above  compounds  yield  more  hydrogen  and  benzene  nuclei  of  a  still 
more  complex  nature,  leading  eventually  to  carbon  itself.  The  molecule  of  solid 
carbon  in  all  probability  consists  of  a  very  large  number  of  carbon  atoms  arranged 
as  a  honeycomb  of  condensed  benzene  nuclei.  These  complex  substances,  still 
containing  some  hydrogen,  are  black  and  infusible,  and  their  physical  properties 
are  very  closely  akin  to  those  of  pure  carbon  itself. 

As  regards  the  extent  of  free  space  in  the  retort  with  varying  types  of  charges, 
G.  P.  Lewis  has  given  the  following  figures  : — 


THE   CARBONIZATION   OF   COAL 


281 


22  inches  by  16  inches  CD  retort,  6  cwt.  charge  ;  space  in  crown  =65  per  cent,  of  volume  of  retort. 

KK 

»  »  »  «  »»  »'  » 

„         „  „        12      „         „  „        „         =32 

Coke  oven  9  feet  by  1  foot  6  inches       ....==  6  „  „  „ 

In  the  Woodall-Duckham  vertical  retort  the  free  space  is  variable,  at  will,  and 
amounts  to  0-7  to  14  per  cent,  of  the  total  volume  of  the  retort. 

As  regards  the  effect  of  varying  the  duration  of  charge  upon  the  products 
obtained,  Ferguson  Bell  gives  the  following  comparisons  : — 


Duration  of 
charge. 

Weight  of 
charge. 

Gas  made 
per  ton. 

Candle  power 
No.  2  Met. 

Calorific  value  per 
cubic  foot. 

B.Th.U. 

Hours. 

Cwt. 

Cubic  feet. 

Net. 

6 

6 

10,594 

16-31 

538-8 

8 

71 

11,245 

15-59 

518-9 

10 

9* 

11,499 

14-53 

488-4 

12 

ll| 

11,463 

14-77 

484-4 

The  principle  of  the  heavy  charge  has  recently  been  carried  to  further  lengths 
by  Mr.  Isaac  Carr,  who  has  installed  at  Widnes  retorts  having  a  cross  section  of  24 
inches  by  20  inches,  and  capable  of  carbonizing  about  a  ton  of  coal  in  twenty-four 
hours. 

To  sum  up,  the  merits  of  the  heavy  charge  as  compared  with  the  results  from 
partly  filled  retorts  may  be  enumerated  as  follows  : — 

(1)  Considerably  curtailed  carbonizing  costs. 

(2)  Less  degradation,  and,  therefore,  less  naphthalene  and  free  carbon. 

(3)  Few  stopped  pipes. 

(4)  More  ammonia. 

(5)  Better  coke  of  a  denser  nature,  and  less  breeze. 

(6)  More  tar  of  a  better  and  thinner  quality. 

(7)  Less  scurf. 

(8)  Less  sulphur  in  the  form  of  CS2,  etc. 

Some  doubt  seems  to  exist  as  to  the  question  of  fuel.  Whilst  some  authorities 
imply  that  the  heavy  charge  is  more  extravagant  in  this  direction,  this  would  by  no 
means  appear  to  be  the  rule.  The  "  make  per  mouthpiece  "  per  day  shows  some 
falling  off,  owing  to  the  fact  that  with  the  heavy  charge  the  final  hours  of  the  period 
are  largely  yielding  only  the  residual  gases  from  the  coke — comparatively  small  in 
volume,  and  which  are  not  evolved  to  the  same  extent  in  the  short  carbonization 
periods.  With  the  heavy  charge,  it  is,  of  course,  essential  that  the  periods  of  charging 
of  the  various  units  should  be  so  arranged  that  the  resultant  mixture  of  gas  obtained 
is  more  or  less  constant  throughout  the  twenty-four  hours. 

THE  TEMPERATURE  THROUGHOUT  THE   CHARGE 

The  temperatures  prevailing  throughout  the  carbonizing  mass  vary  to  some 
extent  with  the  weight  of  the  charge,  and  it  is  generally  found  that  whereas  with  the 


282 


MODERN   GASWORKS   PRACTICE 


light  charge  the  hottest  zone  is  that  in  contact  with  the  bottom  and  sides  of  the 
retort,  with  complete  filling  the  hottest  portion  will  be  that  forming  the  surface 
of  the  coal.  The  pyrometric  observations  of  Bond,  recorded  in  the  proceedings 
of  the  Institution  of  Gas  Engineers,  are  of  considerable  interest  and  throw  much 
light  on  the  conditions  prevailing.  This  investigator  has  shown  that  the  solid 
residue  tends  to  divide  into  two  distinct  layers,  and  he  recorded  temperatures  at 
the  three  zones  (A,  J?and  C,  Fig.  189)  for  varying  periods  of  the  charge.  At  the 

zone  A  the  temperature  at  the  commencement  of 
the  charge  was  1,250°  Fahr.  ;  at  the  end  of  the 
first  two  hours,  when  37  per  cent,  of  the  total  gas 
had  been  evolved,  it  was  1,460°  Fahr.  ;  whilst  after 
four  and  a  half  hours  a  maximum  of  1,850°  was 
attained.  As  regards  the  zone  B,  at  the  centre  of 
the  charge,  after  the  coal  had  been  distilling  for  two 
hours  the  temperature  was  approximately  the  same 
as  at  the  base  of  the  charge,  but  never  exceeded  the 
latter.  At  the  commencement  of  carbonization  the 
temperature  of  the  core — as  would  be  expected — was 
only  830°  Fahr.  These  results  all  refer  to  a  charge  6  inches  in  depth.  Considerable 
variation  was  found  when  the  thickness  of  the  coal  layer  was  increased  to  12  inches. 
In  this  case  the  temperature  of  the  core  at  the  commencement  was  no  more  than  2CO° 
Fahr.,  but  as  carbonization  proceeded  a  gradual  increase  was  noticeable,  until  after 
eight  hours  there  was  a  temperature  difference  of  only  about  50°  Fahr.  between  the 
base  and  the  core  of  the  charge.  At  this  period  the  hottest  portion  of  the  charge 
was  the  surface,  which  had  risen  to  about  1,950°  Fahr. 

The  following  table,  compiled  from  fgures  given  by  G.  P.  Lewis,  gives  a 
useful  insight  into  the  conditions  of  temperature  obtaining  during  an  eight-hour 
charge  : — 


FIG.  189. — TEMPERATURES  AT 
VARIOUS  ZONES  OF  CHARGE. 


Time  after  commencement  of  charge. 

Hours. 

£12345678 

Degrees  Fahrenheit. 

Light  charge        (Bottom     . 

ta  •     i       iu-  i  \  •{   Centre 
(6  inches  thick)  | 
I,  Top     .      . 

1,290 
1,110 
930 

1,360 
1,250 
1,100 

1,460 
1,360 

1,700 
1,650 
1,600 

1,850 
1,900 
1,740 

1,870 
1,830 
1,760 

1,870 
1,830 
1,850 

(  Bottom 
Heavy  charge        1 

1  12  inches  thick)   )  ^  ntre 
V  Top     .      . 

1,110 
200 
1,380 

1,170 
210 
1,470 

1,290 
300 
1,560 

1,380 
410 
1,590 

1,440 

500 
1,620 

1,470 
610 
1,690 

1,560 
1,080 
1,780 

1,690 
1,470 

1,870 

1,890 
1,870 
1,620 

With  regard  to  vertical  retorts  of  the  continuous  type,  at  the  point  of  combustion 


THE   CARBONIZATION   OF  COAL 


283 


the  temperature  is  about  2,400°  Fahr.,  and  at  the  base  of  the  retort  it  is  approxi- 
mately 2,000°  Fahr.  It  must  not  be  lost  sight  of  that  in  the  vertical  retort 
progressive  heating  may  be  employed,  whereas  in  horizontal  systems  this  is  not 
practicable.  By  such  heating,  the  prevailing  temperatures  of  the  various  portions  of 
the  retort  may  be  varied  and  the  charge  subjected  to  differing  intensities  of  heating 
as  it  travels  downwards.  Thus  we  get  the  two  types  of  heating,  namely,  top  and 
bottom,  in  the  first  of  which  the  upper  portions  of  the  retort  are  subjected  to  the 
most  severe  temperatures  (as  in  the  Woodall-Duckham  system),  the  lower  portions, 
being  more  highly  heated  in  other  systems,  such  as  the  Glover- West  and  Dessau. 
The  conditions  prevailing  in  vertical  retorts  are  illustrated  in  Figs.  190  and  19L 
Whilst  in  continuous  systems 
the  relative  positions  of  un- 
carbonized  coal,  the  viscid 
layer  surrounding  it,  and  the 
coke  zone  remain  practically 
constant,  this  is  not  the  case 
with  intermittent  systems,  in 
which  the  pasty  envelope 
gradually  closes  in  towards  the 
centre  of  the  charge.  With 
continuous  charging,  even  if 
top  heating  be  adopted,  the 
upper  portions  of  the  mass 
will  still  be  relatively  cool,  so 
that  the  primary  gases  coming 
away  at  low  temperatures  are 
subjected  to  the  minimum  of 
degradation.  With  intermitt- 
ent working,  however,  it  is 
essential  to  heat  the  base  of 
the  retort  more  highly,  for  in 
this  way  the  lower  portions  of 
coal  are  carbonized  in  advance 
of  the  upper,  and  thus  a  freer 
passage  through  the  central 
core  is  assured.  The  coke, 
moreover,  is  subjected  to  a 

maximum  temperature  just  before  leaving  the  retort,  so  that  a  considerable  pro- 
portion of  the  volatile  matter  is  expelled  from  it.  That  this  is  desirable  is  shown 
by  tests  carried  out  by  Davidson,  who  found  that  even  "  well-burned-ofE  "  coke  will 
give  off  quite  a  large  amount  of  gas.  Taking  an  ordinary  coke  containing  1-97  per 
cent,  of  volatile  matter,  it  was  shown  that  on  further  heating  this  would  yield  an 
additional  quantity  of  gas  equal  to  2,900  cubic  feet  per  ton  of  coke,  the  compo- 
sition of  the  gas  being  as  follows  : — 


Later 
Stages- 


Continuous 
System 

FIG.  190. 


Intermittent  System 


FIG.  191. 


284 


MODERN   GASWORKS   PRACTICE 


Hydrogen 

Methane 

Carbon  monoxide 

Carbon  dioxide 

Nitrogen 


86-8  per  cent. 
2-05       „ 
6-5 
0-6 
4-05 


Coke  from  the  Dessau  retorts  rarely  contains  as  much  as  1 1  per  cent,  of  volatile 
matter. 

THE  TRAVEL  OF  GAS  IN  VERTICAL  RETORTS 

So  far  as  the  path  by  which  the  gas  finds  its  exit  from  the  horizontal  retort  is 
concerned,  when  once  a  ring  of  hot  coke  has  been  formed  around  the  cool  coal  core 
the  only  way  of  escape  for  the  products  is  through  this  heated  zone.  In  both  types 
of  vertical  retorts,  however,  matters  are  different,  and  the  volatile  constituents  may 
leave  either  by  way  of  the  cool  central  core,  or  by  evolution  from  the  outer  layers 
of  the  pasty  envelope  they  may  travel  upward  through  the  heated  coke.  The  former, 
owing  to  the  absence  of  excessive  degradation,  is,  of  course,  the  most  desirable  outlet, 
and  Bueb  is  of  the  opinion  that  with  intermittent  vertical  systems  the  gas  takes 
this  course.  Colman,  however,  who  has  done  much  work  in  connexion  with  the 
problem,  holds  the  view  that  Bueb's  hypothesis  is  only  true  to  a  very  limited  extent, 
except  in  cases  where  no  pasty  envelope  is  formed — as  with  shales  and  non-caking 
coals.  "  Vertical  "  gas  shows  none  of  the  characteristics  of  a  low  temperature  gas,  such 
as  would  be  obtained  if  the  products  took  the  cooler  path.  In  fact,  hydrogen  is 
somewhat  higher  than  is  the  case  with  "  horizontal  "  gas,  ethylene  is  comparatively 
low,  arid  ethane — essentially  a  primary  product — is  entirely  absent.  The  tar,  more- 
over, inclines  towards  a  benzenoid  character.  Colman  corroborated  his  views  by 
analysing  the  gas  from  various  portions  of  the  retort,  with  the  following  results  : — 


Gas  drawn 
from  coal  core. 

Gas  drawn 
from  coke  zone. 

Final  gas 
obtained. 

Hydrogen  .      .            

45  -3  per  cent. 

59-0  per  cent. 

53-5  per  cent. 

Methane      .                  

37-2 

20-2 

28-0 

Carbon  monoxide      .      .      .      . 
Carbon  dioxide                

8-8 
5-9         „ 

12-9 
3-0 

11-9 
3-2 

Unsaturated  hydrocarbons   .      .      .      . 
Oxvcren 

2-0 
nil 

1-9 

nil 

2-3 

nil 

Nitrogen     ......... 

0-6 

3-2 

1-3 

The  marked  resemblance  of  the  final  gas  to  that  obtained  from  the  coke  zone 
will  be  noticed.  Colman  concludes  his  argument  by  stating  that  probably,  on  the 
whole,  the  volatile  products  are  subjected  to  the  influence  of  the  heated  coke  surfaces 
to  a  rather  greater  extent  than  is  the  case  with  horizontal  retorts. 

Vertical  retorts,  though  having  fully  established  their  claims  in  many  directions, 
are  still  passing  through  a  stage  more  or  less  of  evolution,  and  therefore  it  is  inoppor- 
tune to  discuss  their  relative  merits  as  carbonizing  agents  compared  with  the  time- 


THE   CARBONIZATION   OF   COAL 


285 


honoured  horizontal  retorts.  One  cannot  do  better  than  quote  the  views  of  an 
authority  who  has  had  every  opportunity  of  experimenting  with  all  kinds  of  plant. 
His  opinion  is  that  "  on  summing  up  the  respective  balance-sheets,  very  little  differ- 
ence may  be  found  between  the  two  competitive  systems,  and  local  circumstances 
may  settle  the  question  one  way  or  the  other." 


"  STEAMING  "   IN  VERTICALS 

Mention  has  already  been  made  of  the  practice  of  "  steaming  "  as  usually 
adopted  in  the  intermittent  forms  of  vertical  retorts.  The  effect  is  to  swell  the 
gas  yield  to  some  extent  whilst  the  deterioration  in  quality  is  not  marked.  Davidson 
gives  the  following  comparative  analyses  : — 


Without  steaming. 

Steam  for  last  2  hours  of 
12-hour  charge. 

Hydrogen  

55  '2  per  cent. 

55-6  per  cent. 

Methane  
Carbon  monoxie  
Carbon  dioxide  
Unsaturated  hydrocarbons  .... 
Oxvsen 

27-5 
11-0 
2-25       „ 
2-63 
0-43       „ 

27-1 
11-1 
2-2 

2-58 
0-43         „ 

Nitrogen  

i-o 

i-o 

These  figures,  for  the  purpose  of  comparison,  are  reduced  to  1  per  cent,  of  nitro- 
gen content.  The  steaming  gave  an  increase  of  yield  of  280  cubic  feet  of  gas  per 
ton,  whilst  a  decrease  of  4  B.Th.U.  per  cubic  foot  was  found. 

The  figures  of  Drury,  given  below,  enable  a  good  indication  to  be  obtained  of 
the  effect  on  illuminating  power  : — 


Gas  per  ton. 

Illuminating  power. 

Net  calorific  power. 

Charge  unsteamed      .... 
„       steamed    

11,838  cubic  feet 
12,996 

16-86  candles 
16-62      „ 

536  B.Th.U. 
534 

Thus  an  increase  in  "  make  "  of  1,158  cubic  feet  is  obtained  with  practically 
an  unnoticeable  difference  in  quality. 


CHAPTER   XII 

THE  CONDENSATION  OF   COAL   GAS 

ALTHOUGH  the  operation  of  condensation  might  appear  to  be  one  of  extreme  sim- 
plicity, this  is  by  no  means  the  case  ;  for  the  character  of  the  final  products  obtained 
is  appreciably  influenced  by  the  manner  in  which  the  gas  is  dealt  with  at  this  stage. 
Condensation  maybe  best  denned  as  the  reduction  of «the  gas  to  normal  temperatures, 
and  the  simultaneous  removal  of  all  those  substances  which  are  not  permanent  gases 
.at  such  temperatures.  In  the  main,  the  apparatus  employed  for  the  purpose  is  of 
a  simple  nature,  and  merely  embodies  the  principle  of  exposing  large  surface  areas 
to  the  action  of  a  cooling  agent.  On  gasworks  the  cooling  medium  employed  is 
either  air  or  water,  or  both.  The  atmospheric  condenser  was  a  common  feature  of 
gasworks  in  the  past,  and  it  is  still  to  be  found  in  many  of  the  smaller  and  medium- 
sized  works.  As  a  cooling  agent,  however,  water  is  infinitely  more  efficient.  When 
.a  temperature  drop  of  10°  Fahr.  is  required,  the  capability  of  water  (per  square  unit 
of  surface  exposed)  to  bring  about  the  reduction  is  eleven  times  as  great  as  that  of 
air,  and  when  the  temperature  drop  increases  to  50°  Fahr.  the  proportional 
efficiency  is  more  than  200  to  1.  In  addition,  the  water-cooled  condenser  is  easily 
regulated,  so  that  a  more  or  less  constant  outlet  temperature  may  be  obtained  whether 
the  apparatus  is  working  up  to  its  full  capacity  or  not. 

ATMOSPHERIC    CONDENSERS. 

Condensers  of  the  atmospheric  type  are  of  no  stereotyped  construction,  and 
in  the  case  of  some  small  works  are  often  made  up  from  odd  lengths  of  pipe  and 
connexions  which  the  manager  may  have  at  his  disposal.  In  general,  however,  the 
chief  standard  varieties  in  common  use  may  be  classified  as  follows  : — 

(a)  Horizontal  types. 
(6)  Vertical  types. 

(c)  Annular  types. 

(d)  The  battery  condenser. 

The  horizontal  condenser  shown  in  Fig.  192  frequently  takes  the  form  of  an 
extended  foul  main  which  is  carried  in  zigzag  fashion  from  end  to  end  of  one  of  the 
retort-house  walls.  As  blockages  from  naphthalene  or  pitchy  deposits  are  likely 
to  occur  at  times,  it  is  essential  that  flange  connexions  should  be  used,  so  that  clearing 
may  be  easily  effected.  The  condensed  liquids  flow  down  the  sloping  pipes  in  the 

286 


THE   CONDENSATION   OF   COAL   GAS 

same  direction  as  the  gas.  In  the  general  way  this  procedure — when  slow  travel 
is  assured — would  seem  to  be  quite  effective  in  the  removal  of  naphthalene.  In 
•conjunction  with  the  steel  foul  main,  steel  is  also  being  employed  to  some  extent  in 
the  construction  of  condensers.  The  horizontal  condenser  shown  in  the  sketch  is 
constructed  in  spiral  form,  and  differs  from  the  most  simple  type  in  that  it  rests  upon 
its  own  stanchions.  A  common  type  of  vertical  air  condenser  complete  with  gas 
and  tar  outlets  is  shown  in  Fig.  193.  The  annular  atmospheric  condenser  (Fig. 
194)  has  in  the  past  assumed  a  good  deal  of  importance,  and  is  probably  the  most 
satisfactory  example  of  these  types,  in  that  the  intensity  of  cooling  is  to  some  extent 
under  control.  As  can  be  seen  from  the  sketch,  the  gas  passage  in  the  tall  vertical 


FIG.  192. — HORIZONTAL  CONDENSER. 

cylinders  is  annular  in  form,  hence  both  an  inside  and  outside  surface  are  exposed 
to  the  cooling  effect  of  the  air.  The  diagonal  side  pipes  convey  the  warm  gas  to 
the  upper  ends  of  each  annular  cylinder,  and  in  this  way  a  comparatively  strong 
draught  is  caused  to  ascend  the  inner  air  tube.  Butterfly  valves  or  dampers  are 
fitted  to  the  top  of  each  vertical  air  pipe,  so  that  the  amount  of  cooling  can  be  regu- 
lated in  accordance  with  requirements.  These  valves  are  usually  operated  by  means 
of  a  hand  chain  reaching  to  the  ground.  Occasionally  this  type  of  condenser  is 
found  with  the  diagonal  pipes  omitted,  the  cylinders  being  connected  by  short  hori- 
zontal branches,  in  which  case  the  gas  travels  up  and  down  the  cylinders  alternately. 


288 


MODERN   GASWORKS   PRACTICE 


The  annular  condenser  shown  in  the  figure  is  the  improved  Walker  type,  and  may 
be  composed  of  any  number  of  tubes.  It  will  be  noticed  that  the  inner  cylinder  is 
coned,  sc»as  to  increase  the  annular  space  at  the  bottom.  In  this  way  stoppage 
due  to  tarry  deposits  is  avoided.  The  base  of  the  annular  space  is  also  given  a  fall, 
so  that  tar  may  run  away  readily  to  the  seal-pot. 


FIG.  193. — VERTICAL  CON  DENSER. 


The  battery  condenser  (Fig.  195)  is  of  somewhat  novel  construction.  It  con- 
sists of  a  long  and  narrow  box  divided  internally  by  baffle-plates  which  cause  the 
gas  to  take  a  circuitous  course.  The  width  of  the  box  is  usually  about  2  feet,  and 
small  tubes  passing  from  side  to  side  form  the  chief  cooling  surface.  The  ends  of 


FIG.  194. — ANNULAR  CONDENSER. 


289 


290 


MODERN   GASWORKS   PRACTICE 


these  tubes  are  left  open,  so  that  a  current  of  air  readily  passes  through.  In  addi- 
tion, the  obstruction  caused  by  the  tubes  has  some  effect  in  breaking  up  and  throwing 
down  the  tarry  vesicles  suspended  in  the  gas. 

So  far  as  capacity  of  condenser  plant  is  concerned,  the  most  reliable  rule  from 
which  to  form  an  estimate  is  that  which  provides  an  allowance  of  5  square  feet  of 
superficial  area  per  1,000  cubic  feet  of  gas  made  per  diem.  This  is  sufficient  (but 
not  extravagantly  so)  when  cast-iron  mains  and  apparatus  are  employed,  and  may 
be  slightly  reduced  when  wrought  iron  or  mild  steel  is  used.  It  must  be  borne  in 
mind  that  the  figure  given  by  this  rule  includes  (in  addition  to  the  areas  exposed  by 
the  actual  condenser)  the  area  of  all  piping  between  the  outlet  of  the  hydraulic  main 

m 


Gas  Outlet 


o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 


o  o  o 
o  o  o 
coo 
o  o  o 
o  o  o 
o  o  o 


o  c  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 


o  o  o 
coo 

o  o  o 

000 

o  o  o 
o  o  o 


o  o  o 
o  o  o 

000 

o  o  o 
o  o  o 
o  o  o 


o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

000 


Gas  Inlet 


FIG.  195.  —  BATTERY  CONDENSER. 

and  the  inlet  of  the  condenser.     This  is  readily  calculated.     The  following  relate  to 
pipes  commonly  in  use  as  foul  mains  :  — 

6-inch  pipe.     Each  foot  run  exposes  an  area  of  1-57  square  feet. 


9-inch 
12-inch 
15-inch 
18-inch 
24-inch 


2-35 
3-14 
3-92 
4-71 

6-28 


Many  other  rules  exist  for  computing  the  capacity  of  condensers.  One  based 
on  the  quantity  of  coal  states  that  100  to  120  superficial  feet  should  be  allowed  for 
every  ton  carbonized  per  diem.  Another  rule,  based  on  thoroughly  sound  principles, 
but  difficult  of  application  in  practice,  says  that  4  square  feet  of  surface  should  be 


THE   CONDENSATION   OF   COAL   GAS 


allowed  per  gallon  of  water  yielded  per  ton  of  coal.  In  order  to  preclude  the  too 
sudden  condensation  of  gas  there  was  in  past  years  a  generally  recognized  formula 
stipulating  that  of  the  total  length  of  foul  main  20  feet  of  length  per  inch  diameter 
of  the  pipe  should  be  under  cover  in  the  retort  house.  The  rule,  however,  has  lost 
its  significance  in  present-day  practice. 

WATER   CONDENSERS 

Water  condensers  as  now  employed  are  almost  solely  constructed  from  riveted 
mild  steel  plates  (which  form  the  outer  shell)  and  steel  or  wrought-iron  tubes.  There 
are  two  distinct  types  at  present  in  use,  namely  : — 

(a)  Multitubular  condensers. 
(6)  Water-tube  condensers. 

Although  both  types  possess  their  respective  advantages,  it  is  now  generally 
recognized  that,  except  in  cases  where  the  condensing  water  is  exceptionally  clean, 
the  water-tube  condenser  is  to  be  preferred.  The  outstanding  distinction  between 
the  multitubular  and  water-tube  condenser  is  that  in  the  former  the  water  passes 
outside  and  around  the  tubes  which  carry  the  hot  gas,  whereas  in  the  latter  type 


Water 


Gas 


FlG.    196. MULTITUBTTLAR  CONDENSER. 


FIG.  197. — WATER-TUBE  CONDENSER. 


the  opposite  is  the  case.  The  difference  is  clearly  seen  by  reference  to  Figs.  196 
and  197.  It  will  be  realized  that  when  any  deposit  is  likely  to  take  place  it  is  far 
preferable  to  have  this  within  the  tubes,  which  can  be  readily  cleaned,  rather  than 
in  the  chamber  surrounding  them.  Thus  when  only  muddy  water  pumped  from 
rivers  or  canals  is  obtainable  there  should  be  no  hesitation  in  adopting  the  water- 
tube  system.  On  the  other  hand,  if  the  incoming  gas  is  particularly  dirty  and  con- 
tains an  undesirable  quantity  of  heavy  tar  vesicles,  the  outer  chamber  is  liable  to 
obstruction  from  this  cause.  In  the  calculation  of  the  area  of  cooling  surface  required 
it  should  be  remembered  that  the  actual  surface  to  be  considered  is  that  with  which 
the  gas  is  in  contact.  Hence  when  the  gas  travels  inside  a  tube  the  interior  surface 
must  be  taken,  but  when  the  gas  is  surrounding  the  tube  the  exterior  surface  is  con- 
sidered. From  this  it  will  be  seen  that  the  water-tube  type  gives  more  condensing 
area  for  the  same  number  of  tubes.  Mention  has  already  been  made  of  the  com- 


292 

bined  atmospheric  and  water-cooled  condenser.  This  in  reality  amounts  to  nothing 
more  or  less  than  a  condenser  of  the  water- tube  type.  In  this  case  it  will  be  seen 
that  the  outer  casing  is  available  as  an  atmospheric  cooling  surface,  whereas  in  the 
multitubular  condenser  this  function  is  lost,  owing  to  nearly  cold  water  (instead  of 
hot  gas)  being  in  contact  with  the  shell.  J.  S.  Haug  has  pointed  out  that  the  upkeep 
of  the  multitubular  condenser  as  regards  painting  is  much  more  expensive,  due  to 
what  is  commonly  called  "  sweating,"  which  is  occasioned  by  the  condensation  of 
moisture  from  the  air  on  the  cold  shell.  In  the  case  of  the  water-tube  condenser 
the  shell  is  hot,  and  condensation,  therefore,  does  not  occur  in  this  manner. 

So  far  as  the  actual  condenser  capacity  required  for  a  given  works  is  concerned, 
the  general  allowance  for  all  types  of  water-cooled  apparatus  may  be  taken  as  3 
square  feet  of  cooling  surface  per  1,000  cubic  feet  of  gas  passing  per  maximum  diem. 
In  the  case  of  the  multitubular  type  of  condenser  a  deduction  (calculated  on  the  rule 
already  given  for  air-cooled  apparatus)  may  be  made  for  the  surface  of  the  outside 
shell,  whilst  for  all  types  the  length  of  foul  main  should  be  considered,  as  previously 
pointed  out.  To  determine  the  efficiency  of  a  condenser  and  its  ability  to  deal  with 
a  given  set  of  conditions  it  is  necessary  to  consider : — 

(a)  The  average  inlet  temperature  and  the  desired  outlet  temperature. 

(6)  The  condition  of  saturation  of  the  gas. 

(c)  The  rate  of  transmission  of  heat  from  the  surfaces  employed. 

First,  it  has  to  be  recognized  that  the  aqueous  vapour  with  which  the  hot  gas 
is  saturated  accounts  for  by  far  the  largest  share  of  the  total  work  of 
condensation.  This  is  due  to  the  fact  that  the  water  vapour  has  to  be 
deprived  of  considerable  quantities  of  heat,  the  same  applying  in  some 
measure  to  the  liquefiable  hydrocarbons.  A.  F.  Browne  has  estimated  that  of 
the  total  work  of  condensation  87  per  cent,  is  accounted  for  in  removing  aqueous 
vapour,  and  13  per  cent,  in  cooling  permanent  gases  and  in  condensing  liquefiable 
hydrocarbons.  Crude  gas,  although  deprived  of  a  large  portion  of  the  aqueous 
vapour  it  originally  contained,  is  still  in  a  state  of  saturation  when  it  arrives  at  the 
condenser  inlet.  If  this  were  not  the  case  the  process  of  condensation  would  be  a 
trifling  matter.  The  actual  number  of  heat  units  to  be  extracted  can  be  arrived  at 
by  ascertaining  the  weight  of  water  vapour  present  in  the  gas  passing  at  the  inlet, 
and,  similarly,  the  weight  of  water  vapour  present  at  the  outlet.  The  difference  will 
give  the  weight,  of  water  condensed  out  of  the  gas.  This  figure  multiplied  by  the 
thermal  units  to  be  liberated  per  pound  of  water  between  the  inlet  and  outlet  tem- 
peratures will  give  the  total  amount  of  heat  which  is  to  be  eliminated.  The  ability 
of  a  surface  to  transmit  heat  varies  to  some  extent,  not  only  with  the  difference  be- 
tween the  temperatures  involved,  but  with  the  condition  of  the  surface,  i.e.,  whether 
clean  or  coated.  Haug,  in  careful  experiments,  found  that  when  the  difference  in 
temperature  between  the  two  surfaces  (i.e.  the  heat  potential)  was  30°  Fahr.,  the 
heat  transmission  amounted  to  approximately  6  B.Th.U.  per  square  foot  of  surface 
under  average  working  conditions.  It  is  pointed  out,  however,  that  as  temperature 
differences  decrease  the  unit  given  will  slowly  decrease,  and  vice  versa. 


THE   CONDENSATION   OF   COAL   GAS 


293 


Water  In  or  Out 


Gas  In  or  Out 


THE  DESIGN   OF   CONDENSERS 

Several  types  of  water-cooled  condensers  are  in  use  to-day,  but  in  many  cases 
the  difference  is  only  a  matter  of  detail.  Older  patterns  having  cast-iron  shells  are 
still  in  evidence,  but  in  general  the  construction  will  conform  to  that  shown  in  Fig. 
198.  This  condenser  may  be  used  singly  or  in  batteries,  and  some  means  should 
always  be  provided  wherewith  the  flow  of  gas  and  water  may  be  reversed.  So  far 
as  general  dimensions  are  concerned,  the  height  of  the  apparatus  should  be  from  two 
to  five  times  the  diameter.  For  smaller  condensers  2-inch  water  tubes  may  be  em- 
ployed, but  the  3-inch  is  preferable  for  all  larger  types.  A  point  to  remember  is  that 
the  length  of  the  tube  should  not 
be  such  as  to  make  it  structurally 
weak  ;  it  is  as  well  to  confine  the 
ratio  of  length  to  diameter  within 
the  limit  of  80  to  1.  The  larger 
tubes  are  certainly  more  easily  kept 
free  from  stoppage  and  are  more 
readily  cleaned,  but  there  is  some 
limit  to  their  size  in  that  as  the 
diameter  increases  the  cooling  sur- 
face per  unit  area  of  ground  surface 
is  curtailed.  As  regards  length,  it 
is  as  well  to  confine  this  within 
the  limits  of  manufacturers'  stock 
sizes,  otherwise  additional  expense 
will  be  incurred.  The  20-foot  tube 
is,  perhaps,  most  suitable  for  all 
the  larger  condensers.  In  shape 
the  water  condenser  is  nearly 

always  cylindrical, v  this  section  facilitating  the  building  together  of  the  mild  steel 
plates  forming  the  shell.  Moreover,  the  shell  of  the  multitubular  type  has  to 
withstand  the  stresses  due  to  water  pressure,  and  the  cylindrical  shape  is  better 
able  to  do  so.  Only  in  the  case  of  the  largest  condensers  is  it  advisable  to  work 
to  a  rectangular  section,  and  then  only  in  those  instances  in  which  the  saving  of 
ground  space  is  a  consideration.  So  far  as  the  spacing  of  tubes  is  concerned  there 
is  no  hard  and  fast  rule,  but  it  is  as  well  to  remember  that  the  free  space  in  the 
shell  should  not  be  too  greatly  encumbered  ;  otherwise  stoppage  will  quickly  result. 
A  good  basis  to  work  upon  is  that  of  arranging  the  tubes  so  that  they  occupy 
about  18  per  cent,  of  the  total  area  of  the  tube  sheet.  For  water  gas  this  should 
be  increased  to  25  per  cent. 


2"  Tubes  through 

which   Water 
flows  in  opposite 
direction  to  Gas 


n  cr  Out 


To  Seal   Pot 


Water  In  or  Out 

FIG.  198. — TYPICAL  WATER-TUBE  CONDENSER. 


THE  CARPENTER  CONDENSER 

Dr.  Carpenter,  in  dealing  with  large  units  of  gas,  adopts  the  hydraulic  form  of 
condenser,  consisting  of  a  series  of  vertical  cooling  tubes  placed  in  a  cylindrical  vessel 


294 


FIG.  199. — CARPENTER'S  REVERSIBLE  CONDENSER. 


containing  water.     The  tops  and  bottoms  of  the  tubes  are  connected  by  gas  cham- 
bers, and  the  gas  is  made  to  flow  upwards  through  the  tubes  in  one  vessel  and  down- 


THE   CONDENSATION   OF   COAL   GAS 


295 


wards  in  the  second  one.  The  arrangement  of  connexions  and  valves  is  such  that 
the  direction  of  flow  of  the  gas  can  be  reversed  when  desired.  The  pair  of  con- 
densers shown  in  Fig.  199  are  capable  of  dealing  with  about  four  million  cubic  feet 
of  gas  per  diem.  The  cold  water  enters  the  condenser  near  the  point  of  exit  of  the 
cooled  gas  and  flows  up  one  vessel  and  down  the  other  in  a  direction  opposite  to  that 
of  the  gas,  the  outlet  for  the  water  being  near  the  inlet  for  crude  gas.  By  varying 
the  amount  of  circulating  water  a  more  uniform  condensation  is  obtained  under  the 
varying  conditions  of  the  atmosphere  than  is  possible  in  the  ordinary  air  condenser. 
The  tubes  are  3  inches  diameter  inside  and  40  feet  long,  expanded  into  the  top  and 
bottom  tube  plates. 

For  the  purpose  of  eliminating  a  large  portion  of  the  naphthalene  and  for  the 
prevention  of  deposits  in  the  tubes,  tar-spraying  devices  are  fitted  on  the  top  of 
every  tube,  as  shown  in  the  enlarged  detail.  This  consists  of  a  tar-distributing  box 


FIG.  200.— CONNEXIONS  FOR  CARPENTER'S  CONDENSER. 


at  top,  with  scaled  nozzles  provided  with  "  spreaders  "  or  crown  castings  for  distri- 
buting a  thin  film  of  light  tar  down  the  inside  surfaces  of  the  gas  tubes,  the  tar  being 
pumped  into  the  upper  box  for  this  purpose.  The  gas  on  ascending  or  descending 
slowly  through  the  tubes  is  washed  by  this  means,  and  any  deposition  of  naphthalene 
flows  away  along  with  the  condensed  tar  and  liquor  into  a  receptacle  provided  for 
it  in  the  lower  portion  of  the  vessel.  A  steam- jacketed  seal  pipe  and  a  run-off  pipe 
are  provided  as  shown.  The  heated  water,  after  passing  through  the  condensers, 
is  usually  circulated  through  separate  air-cooling  towers  and  used  continuously  over 
and  over  again. 

The  condensers  are  usually  arranged  in  batteries  of  any  number  up  to  twelve, 
and  are  connected  up  so  as  to  be  reversible,  as  shown  in  Fig.  200.  It  will  be  seen 
that  any  possibility  of  error  in  operating  the  valves  is  guarded  against  by  coupling 
up  the  latter  by  means  of  gearing.  The  water  valves  are  arranged  in  precisely  the 
same  manner  as  those  for  the  gas. 


296  MODERN   GASWORKS   PRACTICE 

THE   THEORY   OF   CONDENSATION 

The  primary  object  of  condensation  is  not  merely  the  cooling  of  the  gas  to 
-•atmospheric  temperature,  but  to  ensure  that  the  bulk  of  the  constituents  which  are 
not  permanent  gases  are  separated  out.  By  the  law  of  vapour  pressures  it  is  knowrn 
that  the  saturation  content  of  a  gas  decreases  correspondingly  with  any  reduction 
•of  temperature,  and  that  the  gas  is  unable  to  hold  in  suspension  any  excess  of  vapours 
•above  the  quantity  corresponding  with  its  vapour  pressure  at  the  reduced  tempera- 
ture. Accordingly,  as  the  temperature  of  the  hot  gas  is  reduced  during  its  passage 
"through  the  condenser,  a  considerable  portion  of  the  excess  vapours  (in  the  form  of 
steam  and  liquefiable  hydrocarbons)  is  deposited.  As  has  already  been  pointed  out, 
it  is  the  aqueous  vapour  which  accounts  for  the  greater  portion  of  the  work  of 
cooling  entailed. 

In  the  case  of  coals  containing  a  high  proportion  of  moisture  or  which 
yield  a  large  quantity  of  steam  on  distillation,  the  condensation  apparatus 
may  be  almost  entirely  occupied  in  dissipating  the  heat  arising  from  the 
formation  '  of  steam.  Owing  to  the  extremely  finely  divided  condition  in 
which  many  of  the  particles  are  suspended  in  the  gas  it  is  usually  im- 
possible to  bring  about  their  entire  separation  by  a  reduction  of  vapour  pressure 
by  cooling.  For  this  reason  the  gas  is  frequently  caused  to  undergo  mechanical 
treatment  with  a  view  to  removing  all  traces  of  solid  or  liquid  matter  before  its 
arrival  at  the  wet  purification  plant.  Gradual  cooling,  with  the  strict  avoidance 
of  "  shock,"  is  generally  looked  upon  as  the  ideal  to  be  secured,  for  in  such  cases  the 
hydrocarbons  are  thrown  down  in  sequence,  and  there  is  but  slight  danger  of  depriving 
the  gas  of  a  portion  of  the  more  valuable  constituents  which  it  is  capable  of  retaining 
at  normal  temperatures.  In  connexion  with  this  point  Butterfield  says  that  with 
rapid  cooling  supersaturation  of  the  gas  with  certain  condensible  vapours  occurs, 
whilst  other  less  readily  condensible  constituents  are  dissolved  or  mechanically 
abstracted  by  the  flushing  action  of  the  condensate.  He  points,  moreover,  to  the 
probability  of  the  selective  action  of  radiant  heat  coming  into  play,  and  says  that 
radiation  from  relatively  cool  walls  lowers  the  temperature  of  the  liquid  and  solid 
particles  and  the  more  complex  gases,  whereas  more  permanent  gases  are  unaffected 
by  it,  and  are  cooled  only  by  contact  with  cool  surfaces. 

In  considering  the  principles  of  condensation,  the  question  of  the  removal  of 
aqueous  vapour  may  be  dismissed,  as  it  is  inevitable  that  the  whole  of  this  should  be 
eliminated,  with  the  exception  of  that  portion  with  which  the  gas  is  saturated  at 
normal  temperatures.  So  far  as  the  hydrocarbon  condensate  is  concerned,  it  is  of 
advantage  to  sub-divide  this  in  the  following  manner  : — 

(a)  Heavy  tars. 

(6)  Medium  tars. 

(c)  Light  tars  and  oil  fog. 

Of  the  total  quantity  of  tar  obtained,  about  60  to  65  per  cent,  will  be  deposited 
in  the  hydraulic  main,  and  this  portion  is  largely  of  a  heavy  character.  The  medium 
tars,  of  a  somewhat  lower  specific  gravity,  are  the  next  constituents  to  be  thrown 


THE   CONDENSATION   OF   COAL   GAS  297 

down.  The  greater  pprtion  of  these  will  be  accounted  for  during  the  passage  of  the 
products  through  the  main  connecting  the  hydraulic  with  the  condenser,  whilst  the 
lighter  tars  and  extremely  fine  vesicles  known  as  the  "  oil  fog  "  may  travel  con- 
siderably further.  In  cases  where  condensation  capacity  is  insufficient  or  the  appar- 
atus is  improperly  controlled,  considerable  quantities  of  the  heavier  tar  fog  will  be 
found  to  travel  forward  to  the  scrubbers,  so  that  eventually  stoppage  occurs.  From 
the  point  of  view  of  the  retention  in  the  gas  of  the  maximum  quantity  of  the  hydro- 
carbons, the  slow  travel  and  gradual  temperature  drop  associated  with  the  horizontal 
atmospheric  condenser  cannot  be  improved  upon.  In  general,  the  temperature  of 
the  gas  in  the  hydraulic  main  varies  between  140°  and  160°  Fahr.  Although  this 
temperature  is  below  the  boiling  point  of  the  suspended  tarry  vapours  the  latter  are 
prevented  from  depositing  owing  to  their  being  carried  forward  mechanically  by  the 
moving  bulk  of  gas.  The  constituents  most  liable  to  deposition  are  benzene,  toluene, 
and,  to  some  extent,  xylene,  which  have  an  important  effect  on  the  ultimate  illu- 
minating power  of  the  gas.  A  well-established  rule  of  condensation  states  that  the 
minimum  temperature  to  which  gas  is  reduced  should  not  be  lower  than  50°  Fahr. 
Dr.  Carpenter  has  stated,  however,  that  rapid  condensation  with  a  comparatively 
big  temperature  drop  has  been  shown  in  practice  to  have  very  little  effect  on  illuminat- 
ing power.  The  experiments  which  this  authority  conducted  were  carried  out  with 
gas  which  had  been  subjected  to  an  extremely  sharp  drop  of  from  150°  Fahr.  to  40° 
or  50°  Fahr. 

The  whole  problem  of  condensation  turns  on  the  point  as  to  the  affinity  pos- 
sessed by  tar,  both  in  the  liquid  and  "  fog  "  conditions,  for  absorbing  certain  low 
boiling  hydrocarbons  present  in  the  gas.  Gas  as  it  leaves  the  hydraulic  main  may 
be  looked  upon  as  being  saturated  with  naphthalene,  although  with  modern  systems 
of  carbonization  and  heavy  charges  the  quantity  present  has  been  considerably 
reduced.  There  is  little  doubt  that  the  heavier  tars  and  tar  "  fog  "  with  which  the 
gas  is  in  contact  in  the  initial  lengths  of  the  foul  main  possess  a  marked  affinity  for 
naphthalene.  At  the  same  time  prolonged  contact  must  inevitably  result  in  the 
absorption  of  valuable  low-boiling  constituents.  Authorities  on  condensation  are, 
therefore,  chiefly  in  conflict  as  to  whether  gas  and  tar  should  be  separated  at  the 
earliest  possible  moment,  or  whether  prolo'nged  contact  between  the  two  should  be 
permitted.  As  already  stated,  the  heavy  tars  and  high-boiling  constituents  are 
mostly  separated  out  in  the  hydraulic  main,  although  some  portion  of  these  is  carried 
still  farther  forward  by  mechanical  action.  There  can  be  little  dispute,  however, 
that  such  tars  are  detrimental  from  the  point  of  view  of  the  illuminating  power,  and 
should  be  isolated  from  the  gas  with  all  possible  speed.  For  the  same  reason  a  tar 
seal  in  the  hydraulic  main  is  to  be  avoided.  The  solvent  action  of  the  heavy  tar 
vesicles  becomes  more  pronounced  as  the  temperature  drops.  Thus,  removal  of  the 
heavy  fog  at  an  early  stage  is  probably  desirable,  leaving  the  lighter  qualities  to  exert 
their  action  as  a  naphthalene  solvent. 

Colman  states  that  heavy  tar  fog  when  allowed  to  go  forward  to  the  condensers 
affects  the  removal  of  the  naphthalene  solvents  in  two  ways — one  favourably  and 
the  other  adversely.  On  the  one  hand,  it  removes  from  the  gas  the  vapours  of  the 


298 


MODERN   GASWORKS   PRACTICE 


light  oils,  and  thus  tends  to  prevent  them  from  reaching  the  cold  end  of  the  con- 
denser, where  their  action  on  naphthalene  would  be  most  pronounced.  On  the  other 
hand,  such  fog  as  gets  forward  to  the  cold  end  mixes  with  the  light  oils  which  separate 
there,  thus  increasing  their  content  of  naphthalene  and  impairing  their  ability  to 
take  up  more  of  this  substance.  The  complete  removal  of  naphthalene  can  only  be 
affected  by  the  action  of  solvents  which  are  not  already  saturated  with  the  product. 
It  would  seem,  however,  that  one  of  the  most  effective  methods  of  dealing  with  the 
crude  gas  is  to  eliminate  the  heavy  tars  and  heavy  fog  at  an  early  stage,  and  to  ensure 

the  passage  of  the  light  oil  fog 
as  far  forward  as  the  outlet  of 
the  condenser.  Some  form  of 
mechanical  action  has  the  most 
effective  results  in  breaking  up 
and  throwing  down  the  heavier 
vesicles,  and  Colman  has  success- 
fully applied  the  principle  of  cen- 
trifugal force  in  his  "  Cyclone  " 
apparatus.  This  machine,  shown 
in  Fig.  201,  is  usually  interposed 
in  the  foul  main  at  a  point  about 
half-way  between  the  hydraulic 
main  and  the  condensers.  It  con- 
sists of  a  wrought  or  cast-iron 
cylinder,  to  the  bottom  of  which 
is  connected  an  inverted  conical 
chamber,  having  a  seal  pipe 
attached  to  its  lower  end.  The 
gas  inlet  is  rectangular  and  enters 
the  cylinder  at  a  tangent.  It 
contains,  moreover,  a  flap  valve 
by  means  of  which  the  velocity 
of  the  gas  is  regulated.  A  whirl- 
ing motion  is  thus  set  up,  so  that 
the  tarry  vesicles  are  thrown 
against  the  sides  of  the  vessel  by 
centrifugal  force,  broken  up,  and  run  off  to  the  seal.  The  gas,  meanwhile,  finds  its 
outlet  by  way  of  the  central  vertical  pipe.  In  one  instance  it  was  found  that  in 
passing  through  the  separator  the  gas  gave  up  about  3-^-  gallons  of  liquid  per  10,000 
cubic  feet,  of  which  60  per  cent,  was  tar  and  40  per  cent,  liquor.  This  indicates  that 
the  amount  of  tar  fog  present  was  2  gallons  per  10,000  cubic  feet.  It  resembled  a 
thin  liquid  oil  tar  of  the  nature  of  that  produced  in  the  manufacture  of  water  gas. 
The  extractor  is  made  in  sizes  varying  from  3  feet  to  10  feet  in  diameter. 

The  advocates  of  the  retention  of  the  heavy  tars  in  contact  with  the  gas  point 
out  that  as  the  temperature  falls  the  disposition  of  the  tar  to  absorb  naphthalene 


FIG.  201. — COLMAN'S  "CYCLONE"  TAB  EXTRACTOR. 


THE   CONDENSATION   OF  COAL   GAS 


increases,  hence  contact  at  the  lower  temperatures  is  desirable.  At  the  same  time 
it  must  be  remembered  that  there  is  a  corresponding  increase  in  the  capacity  of  the 
tar  for  absorbing  the  low-boiling  constituents.  In  some  cases  the  "  counter- current  " 
principle  has  been  introduced  ;  that  is  to  say,  the  tar  thrown  down  in  the  condensers 
is  run  backwards  towards  the  hydraulic  main,  so  that  gas  and  tar  are  travelling  one 
against  the  other.  In  Dr.  Carpenter's  system  tar  is  sprayed  down  the  individual 
condenser  tubes  ;  in  addition,  more  or  less  abrupt  condensation  is  arranged  for,  so 
that  the  naphthalene  is  eliminated  and  washed  out  of  the  apparatus  by  the  tar. 

At  Brunswick  gasworks  a  regular  system  of  tar  washing  has  been  instituted  for 
the  purpose  of  removing,  not  only  naphthalene,  but  a  portion  of  the  sulphur  com- 
pounds as  well.  Tar  from  an  overhead  tank,  after  undergoing  nitration,  is  made  to 
fall  in  fine  streams  down  the  annular  space  of  the  condenser  limbs.  The  cold  inflowing 
tar  chills  the  gas,  forming  a  fog,  which  is  removed  by  the  descending  stream  together 
with  almost  all  the  naphthalene,  the  greater  part  of  the  CS2,  and  a  part  of  the  H2S. 
The  approximate  quantity  of  tar  used  is  3|  gallons  per  minute,  which  reduces  the 
temperature  of  3,500  cubic  feet  of  gas  from  122°  Fahr.  to  86°  Fahr.  It  is  stated, 
moreover,  that  the  illuminating  and  calorific  values  of  the  gas  are  only  affected 
favourably  by  the  treatment. 

Whatever  methods  may  be  employed  in  the  condensation  of  coal  gas,  it  must 
be  remembered  that  illuminating  power  has  in  the  present  day  lost  much  of  its  former 
significance  ;  hence  the  retention  in  the  gas  of  the  maximum  quantity  of  low-boiling 
constituents  is  not  so  imperative.  The  greater  the  proportion  of  these  hydrocarbons 
retained  in  the  gas,  however,  the  greater  will  be  the  latitude  afforded  for  attaining 
high  gas  makes  ;  and  from  the  point  of  view  of  economics  the  valuable  constituents 
should  be  retained  in  the  gas,  and  any  surplus  spread  over  a  greater  volume. 


On  coke-oven  works 
it  is  customary  in  some 
cases  to  wash  the  gas  for 
the  removal  of  the  sus- 
pended tar.  In  the  Otto- 
Hilgenstock  system  the 
vesicles  are  actually 
thrown  down  by  spray- 
ing the  gas  coming  from 
the  foul  main  with  more 
tar,  as  shown  in  Fig.  202. 
In  spite  of  the  many 
mechanical  appliances 
now  to  be  had,  the  com- 
plete removal  of  all  traces 
of  tar  from  coal  gas  is 
rarely  effected  before  the 


Gas  Inlet  from 

-**Q  -*- 

bs 

1 

I 

/ 

s 

/ 

Tar  Spray 


Gas  Outlet 
to  Exhauster 


Tar  Pump 


FIG.  202,— TAB  SPRAY. 


.300 


MODERN   GASWORKS   PRACTICE 


wet  purification  plant  is 
reached,  and  the  most  success- 
ful means  for  attaining  this 
end  would  still  seem  to  be  that 
of  bubbling  the  cooled  gas 
through  a  bath  of  liquid,  rather 
than  by  the  introduction  of 
apparatus  embodying  the 
principle  of  "  wire-drawing  " 
or  friction.  Of  the  tar  extrac- 
tors operating  on  the  latter 
principle,  the  Pelouze  and 
Audouin  is  probably  the  most 
generally  utilized.  The  ma- 
chine consists  of  an  outer 
cylindrical  casing  with  the  gas 
inlet  entering  through  the 
centre  of  the  base.  A  bell, 
suspended  from  an  overhead 
pulley  (or  in  later  designs 
from  a  central  shaft,  as  shown 
in  Fig.  203)  passes  over  the 
inlet  pipe  and  has  its  base 
sealed  in  liquor.  The  weight 
of  the  bell  is  counterbalanced 
by  loading  the  wheels  on  the  shaft,  as  shown.  This  floating  bell  is  composed 
of  a  cast-iron  polygonal  top,  having  cast-steel  posts  depending  from  each  corner. 
The  spaces  between  the  posts  are  filled  in  with  bundles  of  perforated  and  slotted 
plates  spaced  a  short  distance  apart,  the  perforations  being  so  arranged  as 
thoroughly  to  baffle  and  break  up  the  gas  on  its  outward  passage.  Safety  valves 
are  fitted  on  the  drum  top  so  that  in  the  event  of  the  suspension  chain  breaking  a 
gas  outlet  will  be  provided.  The  action  of  the  machine  is  automatic,  in  that  the 
extractor  surface  exposed  to  the  gas  varies  in  accordance  with  the  quantity  of  gas 
passing  through  the  mains. 

A  novel  method,  embodying  the  use  of  electricity,  has  been  recently  experi- 
mented with  in  America,  and  has  shown  itself  to  be  perfectly  effective  when  operated 
on  a  fairly  large  practical  scale.  The  principle  introduced  has  been  borrowed  from 
methods  employed  in  connexion  with  smelter  furnaces,  where  it  has  been  customary 
to  bring  about  precipitation  of  *solid  suspended  particles  escaping  with  the  gases  by 
means  of  a  direct  current  high-tension  electrical  discharge.  The  investigators  have 
shown  that  under  certain  conditions  it  is  possible  to  throw  down  the  suspended  tarry 
vesicles  in  crude  coal  gas  under  identical  conditions.  The  apparatus  employed 
consists  essentially  of  specially  constructed  electrodes  suspended  within  a  gas-tight 
•chamber  (Fig.  204).  The  chamber  is  composed  of  a  cast-iron  inverted  U-tube, 


FIG.  203. — "  P  AND  A  "  TAR  EXTRACTOR. 


THE   CONDENSATION   OF   COAL   GAS 


301 


-0  — 


constructed  from  8-inch  pipe  covered  on  the  outside  with  a  jacket- 
ing of  felt.  Each  of  the  arms  of  the  U-tube  is  9  feet  long,  and 
these  form  precipitating  chambers.  An  electrode  is  suspended 
from  the  apex  of  each  arm,  and  is  made  up  from  two  cast-iron 
discs  connected  together  by  a  light  piece  of  gas  pipe,  while  ex- 
tremely fine  discharge  wires  are  afterwards  stretched  from  disc  to 
disc.  The  discs  are  4  inches  in  diameter,  and  each  electrode — of 
the  squirrel-cage  pattern — has  an  effective  length  of  5  feet  8  inches. 
So  far  as  contact  time  is  con- 
cerned, it  is  estimated  that  the 
speed  of  the  gas  passing 
through  the  electrode  cham- 
bers is  about  30  feet  per 
second,  and  the  experiments 
have  shown  that  the  time  of 
exposure  to  the  electrical  dis- 
charge, which  is  under  half  a 
second,  is  ample  for  the  re- 
moval of  the  last  visible  traces 
of  tar.  In  the  latest  type  of 
apparatus  the  difference  of 
potential  between  the  wires 
and  the  grounded  pipe  is  kept 
at  20,000  volts.  Incidentally,  it  has  been  found  that  in  addition  to  bringing 
down  the  whole  of  the  tar  this  electrical  purifier  has  certain  desirable  effects 
in  the  direction  of  minimizing  the  trouble  arising  from  the  deposition  of  naph- 
thalene. For  tar  removal  the  apparatus  has  been  interposed  at  a  point  where  the 
temperature  is  in  the  neighbourhood  of  175°  Fahr. — that  is,  at  a  very  early  period 
in  the  foul  main.  Where  naphthalene  exists  in  the  crystalline  state  the  solid  par- 
ticles may  be  expelled  in  the  same  manner  as  the  vesicles  of  tar.  For  naphthalene 
removal,  however,  a  second  electrode  is  placed  at  a  point  where  the  temperature  is 
at  its  lowest. 


From  Exhauster 


To  Secondary 
Condenser 


FIG.  204. — ELECTRICAL  DISCHARGE  APPARATUS. 


To  the  majority  of  engineers  the  naphthalene  question  is  still  one  of  extreme 
importance,  chiefly  owing  to  the  fact  that  no  definite  solution  has  been  reached. 
Modern  methods  of  carbonization  have  certainly  tended  to  lessen  the  trouble  caused 
by  naphthalene,  but  the  whole  problem  stands  on  unsatisfactory  ground — so  much 
so  that  a  method  which  is  effective  at  one  works  may  be  absolutely  useless  at  another. 
In  recent  years,  however,  it  has  become  usual  to  employ  special  solvents,  to  the 
action  of  which  the  gas  is  subjected  before  travelling  to  the  district  mains.  Paraffin, 
anthracene  oil,  and  water-gas  tar  are  the  most  common  washing  agents  made  use 
of  ;  but  in  all  cases  some  reduction  in  illuminating  power  will  be  noticeable  until  the 
medium  employed  has  become  saturated  with  the  low-boiling  hydrocarbons  (i.e. 


302 


MODERN   GASWORKS   PRACTICE 


benzene,  toluene,  and,  to  some  extent,  xylene),  which  it  removes  from  the  gas.  In 
cases  where  this  temporary  deprivation  of  candle-power  might  give  rise  to  incon- 
venience it  is  advisable  to  pre-benzolize  the  washing  medium  by  adding  about  5  per 
cent,  of  benzol  to  it.  Works  manufacturing  carburetted  water  gas  will  find  the  tar 
from  this  plant  the  most  economical  solvent  to  employ,  although  the  final  traces  of 
naphthalene  are  seldom  removed  by  it.  The  gas  may  be  washed  in  the  crude  or 
purified  state,  or  either  hot  or  cold  ;  and  where  a  horizontal  washer  scrubber  is  in  use 
it  may  be  so  arranged  that  a  few  of  the  bays  contain  water-gas  tar,  whilst  the  remain- 
der are  operated  with  water  in  the  usual  manner.  Another  means  is  to  set  aside 
one  of  the  scrubbers  for  naphthalene  removal  purposes,  and  to  circulate  water  gas 
through  the  tiers  of  coke  or  boards  until  the  tar  has  become  fully  saturated  with 
the  hydrocarbon.  Extensive  contact  of  this  kind  is  certainly  effective  from  the 
naphthalene  standpoint,  but  some  material  reduction  in  the  illuminating  power 
must  be  expected  when  a  fresh  bulk  of  tar  is  put  into  circulation.  Probably  the 
most  desirable  treatment  is  that  of  washing  with  anthracene  oil  just  prior  to  the 
gas  entering  the  holder. 

The  amount  of  naphthalene  in  coal  gas  varies  considerably,  in  accordance  with 
the  coals  made  use  of  and  the  system  of  carbonization  employed.  The  following, 
however,  may  be  taken  as  exemplifying  the  average  quantities  at  the  various  stages 
of  manufacture  : — 


Inlet  of  condensers 

Outlet 

Outlet  of  purifiers 


80  grains  per  100  cubic  feet. 

20-25      „ 

10-15 


By  the  time  the  gas  leaves  for  the  district  the  amount  will  probably  be  reduced 
to  from  6  to  8  grains,  unless  some  means  of  removing  it  is  employed.  Butterfield 
has  compiled  the  following  interesting  table,  which  shows  the  amount  of  naphthalene 
in  gas  saturated  with  the  substance  at  various  temperatures  : — 


Temperature. 

Per  cent,  of  naphthalene 
by  volume. 

Pounds  of  naphthalene  con- 
tained in  1,000,000  cubic 
feet  of  gas. 

120°  Fahr.  ........ 
70° 

0-1070 
0-0070 

325-0 
23-5 

60°  „  
40°  „  .......  . 
32°  „  ........ 

0-0047 
0-0028 
0-0008 

16-0 
9-5 

2-8 

It  is  pointed  out,  moreover,  that  the  above  figures  indicate  that,  apart  from 
supersaturation  effects,  a  million  cubic  feet  of  gas  cooled  from  68°  Fahr.  to  50°  Fahr. 
may  deposit  in  the  works  mains  about  14  Ib.  of  naphthalene.  When  it  is  remembered 
that  10  grains  of  naphthalene  will  completely  block  a  |-inch  pipe  for  a  length  of 
about  1  foot,  the  effect  of  this  bulk  of  naphthalene  will  be  realized. 


THE   CONDENSATION   OF   COAL   GAS  303 

The  methods  which  have  been  introduced  for  the  reduction  or  entire  elimination 
of  naphthalene  may  be  summarized  as  follows  : — 

(a)  By  employing  condensed  tars  and  tar  or  oil  "  fog  "  to  its  best  advantage. 
(&)  By  "  shock,"  i.e.  abrupt  cooling. 

(c)  By  carburation,  or  spraying  special  solvents  into  the  mains. 

(d)  By  washing  with  special  solvents. 

(e)  By  desiccating  the  gas. 

(/)   By  causing  deposition  with  the  aid  of  electrical  discharge  (see  page  301). 

With  regard  to  method  (e),  one  of  the  early  investigators,  Bremond,  found  that 
naphthalene  is  set  free  wherever  there  is  condensation  of  the  aqueous  vapour  in  the 
gas,  that  its  deposition  is  preceded  by  the  deposition  of  water,  and  that  gas  deprived 
as  far  as  possible  of  aqueous  vapour  does  not  deposit  naphthalene.  Bremond,  there- 
fore, dried  his  gas  by  passing  it  through  a  vessel  containing  a  desiccating  material. 
A  good  deal  of  success  attended  this  method,  but  the  experiments  were  carried  out 
on  only  a  comparatively  small  scale.  At  the  present  time  the  water  in  station  meters 
and  gas-holders  is  often  covered  with  a  film  of  oil  so  as  to  prevent  further  saturation 
of  the  gas.  Condensation  in  the  mains  (probably  attended  by  the  deposition  of 
naphthalene)  is  thus  curtailed.  Carburation  with  solvents  (method  c)  was  introduced 
by  Botley,  who  injected,  by  means  of  a  special  spray,  about  4  gallons  of  thoroughly 
atomized  paraffin  oil  per  million  cubic  feet  of  gas.  This  investigator  found  that  the 
oils  most  suited  for  enriching  purposes  are  not  the  best  for  naphthalene  washing  ; 
thus  petroleum  is  more  efficient  than  a  light  spirit  or  benzol.  When  the  system  is 
in  use,  a  dark  green  oil  is  pumped  from  the  street  syphons,  this  being  recovered  and 
made  use  of  on  the  works  for  lubrication,  or,  in  some  cases,  recarburetting.  The 
recovered  portion  amounts  to  about  25  per  cent,  of  the  original  quantity  used.  The 
temperature  at  which  the  oil  mist  is  injected  is  of  some  importance,  a  degree  or  two 
above  that  of  the  gas  in  the  mains  being  most  satisfactory.  Colson  adopted  the 
practice  of  washing  the  gas  in  a  Livesey  washer  (see  page  334)  with  an  oil  specially 
prepared  from  tar.  The  distillate  used  had  an  average  specific  gravity  of  0-996  and 
was  obtained  at  temperatures  between  340°  and  420°  Fahr.,  being  of  the  nature  of 
•creosote.  It  was  not  necessary  to  fill  the  washer  completely  with  the  solvent,  and 
-a  depth  of  a  few  inches  on  the  surface  of  the  liquor  was  found  to  be  sufficient.  Creo- 
sote oil  of  a  heavy  nature  is  now  largely  used  for  "  stripping  "  the  benzene  from  the 
gas  produced  on  coke-oven  works.  Some  caution  is  therefore  necessary  in 
its  employment  for  washing  purposes  on  gasworks,  for  it  is  quite  possible 
to  reduce  the  illuminating  power  to  7  or  8  candles  in  this  way.  Leather 
made  use  of  this  oil  for  eliminating  naphthalene,  but  took  the  precaution 
to  pre-benzolize  it  first.  Once  saturated  with  naphthalene  the  oil  may  be 
distilled,  when  the  benzene  and  toluene  are  recovered  with  the  light  oils. 
The  naphthalene  is  then  eliminated  by  means  of  live  steam,  and  the  residue 
remixed  with  the  benzene  distillate  and  returned  to  the  washer.  K.  de  la  Boulaye 
experimented  with  a  number  of  substances,  ranging  from  methyl  and  ethyl  alcohol 
to  heavy  oils,  in  order  to  determine  their  relative  merits  as  solvents  for  naphthalene. 
Finally  he  concluded  that  the  best  remedy  for  naphthalene  was  abrupt  condensation, 


304 

and  the  ultimate  use  of  a  benzol  or  heavy  oil  spray  in  the  mains  before  the  gas  left 
for  the  district.  The  practice  adopted  by  Ferguson  Bell  is  somewhat  uncommon. 
The  gas  whilst  in  a  warm  state  is  washed  with  warm  tar  ;  and,  at  the  outlet  of  the 
washers  and  scrubbers,  further  treatment  with  a  naphtha  oil  is  accorded  it. 

The  introduction  of  carburetted  water  gas  has  undoubtedly  gone  some  con- 
siderable way  towards  lessening  the  naphthalene  evil,  although  opinions  differ  con- 
siderably as  to  its  utility  in  this  direction.  A  great  deal,  however,  depends  upon 
the  method  of  manufacture  of  the  water  gas,  and  more  particularly  upon  the  tem- 
perature to  which  it  is  subjected  during  its  passage  through  the  superheater.  If  the 
superheater  is  maintained  at  temperatures  much  above  the  normal  the  gas  will  be 
largely  deprived  of  its  solvent  properties,  owing  to  the  over-cracking  of  the  oils  upon 
which  these  properties  depend. 


CHAPTER   XIII 
EXHAUSTING  MACHINERY 

ALTHOUGH  the  exhauster  has  only  come  into  general  use  during  comparatively 
recent  years  its  invention  extends  back  to  quite  the  early  days  of  gaslighting,  the 
scientific  apparatus  employed  to-day  having  been  gradually  evolved  from  an  exceed- 
ingly crude  beginning.  The  necessity  for  some  such  apparatus  first  became  apparent 
when  the  original  cast-iron  retorts  began  to  give  way  to  those  made  from  more 
porous  substances.  The  idea  of  drawing  off  the  gas  from  the  retorts  by  the  creation 
of  a  vacuum  seems  to  have  first  occurred  to  an  engineer  named  Grafton,  about  the 
year  1839.  The  machine  which  this  investigator  made  use  of  was  extremely  ineffi- 
cient, consisting  of  an  ordinary  wet  gas  meter  with  the  inlet  and  outlet  reversed 
and  having  the  drum  driven  by  power.  The  notion,  however,  paved  the  way  for 
more  suitable  apparatus,  with  the  result  that  ten  years  later  the  exhauster  had 
become  a  familiar  feature  of  the  larger  works.  Nowadays,  this  machine,  in  various 
forms,  is  to  be  found  on  all  gasworks  with  the  exception  of  the  very  smallest,  where 
the  cost  of  installing  and  operating  it  would  not  be  commensurate  with  the  saving 
entailed  by  its  introduction.  Where  the  limit,  so  far  as  the  size  of  the  works  is 
concerned,  should  be  placed  is  a  matter  for  argument.  It  is  frequently  stated  that 
any  works  making  two  million  cubic  feet  of  gas  or  over  per  annum  can  profitably  instal 
exhausting  plant.  When  faced  with  actual  facts,  however,  such  a  proposition 
does  not  bear  examination,  and,  unless  exceptional  circumstances  intervene,  the 
use  of  the  exhauster  on  works  making  less  than  four  or  five  million  cubic  feet  per 
annum  is  not  to  be  recommended. 

Consideration  of  an  actual  case  is  sufficient  to  emphasize  this  point.  For 
instance,  consider  a  works  making  five  million  cubic  feet  per  annum.  When  working 
without  an  exhauster  the  gas  made  per  ton  of  coal  would  probably  average  9,500 
cubic  feet,  whilst  the  introduction  of  the  exhauster  might  account  for  an  increased 
yield  of  from  800  to  1,000  cubic  feet.  In  consequence,  the  coal  consumed  annually 
would  be  reduced  from  525  to  480  tons,  i.e.  a  saving  of  45  tons. 

Capital  Outlay  : —  £    a.  d. 

Engine,  exhauster,  valves,  foundation 80     0     0 

N.B. — If  no  building  is  available  for  this  plant,  an  additional  outlay  (say  £30) 
would  be  entailed. 

305  v 


306  MODERN   GASWORKS   PRACTICE 

Charges  to  be  met  (annual) : —  £    s.  d. 

Interest,  depreciation,  repairs,  and  renewals,  14  per  cent,  on  £80         .        :.  .     11     4     0 

Gas  consumed  by  engine,  say  3,000  cubic  feet  per  week  at  2s.,  cost  into  holder  .     15  12    0 

Oil,  stores,  etc.,  per  week  1*.  Qd.          .          .          .          .          .         .  3  18     0 


£30  14     0 


Resultant  Saving  : —  £    s.  d. 

45  tons  of  coal  at  net  cost  price  (after  allowing  for  residuals)  of  12s.  Qd.  28     3     0 

Wear  and  tear  on  carbonizing  plant,  .owing  to  reduced  quantity  of  coal  used, 

at  Is.  6d.  per  ton         .         .         .         ...         .         .         .         .370 


£31  10    0 

The  balance,  it  will  be  noticed,  is  extremely  small,  although  a  good  deal  will 
depend  upon  the  distance  of  the  works  from  a  point  of  delivery  for  materials,  and 
consequently  the  price  at  which  coal  can  be  obtained  at  works.  No  saving  of  labour 
can  be  contemplated,  for  on  works  of  such  a  size  a  single  man  only  is  employed 
for  carbonization.  Moreover,  the  question  of  labour  may  operate  against  the  em- 
ployment of  the  exhauster,  owing  to  the  necessity  for  the  man  in  charge  having 
some  knowledge  of  mechanical  plant.  On  the  other  hand,  the  exhauster  offers 
undoubted  advantages  in  such  directions  as  the  control  of  illuminating  power, 
the  reduction  of  scurf,  etc. 

Exhausters  now  employed  on  gasworks  are  almost  universally  of  the  rotary 
type,  although  those  operating  on  the  reciprocating  principle  and  designed  on  the 
lines  of  an  ordinary  steam  pump  were  in  common  use  in  days  when  the  rotary 
machine  had  not  been  brought  to  its  present  stage  of  perfection.  Primarily,  the 
function  of  the  exhauster,  in  whatever  form  it  may  be  used,  is  that  of  withdrawing 
the  gas  from  the  retorts  by  the  creation  of  a  vacuum,  to  avoid  the  formation  of  an 
excessive  pressure  therein,  and  eventually  to  propel  the  gas  through  the  remainder 
of  the  apparatus  and  into  the  holders,  thus  causing  the  latter  to  rise.  So  far  as  the 
conditions  of  the  operation  of  the  exhauster  are  concerned  the  vacuum  induced  on 
the  inlet  must  be  sufficient — 

(a)  To  overcome  the  seal  on  the  dip-pipe. 

(6)  To  overcome  frictional  losses  arising  from  the  passage  of  the  gas  along  the 
foul  main. 

(c)  To  overcome  the  resistance  offered  to  the  gas  by  the  condenser. 

In  normal  working  and  when  dry  mains  are  not  in  use,  the  hydraulic  seal  amounts 
to  about  half  an  inch,  whilst  the  frictional  losses  in  the  foul  main  may  be  equal  to 
1  inch  of  water  pressure,  and  the  resistance  of  the  condensers  to  2  inches.  Accord- 
ingly, it  is  usual  to  maintain  an  average  vacuum  of  about  4  inches  of  water  at  the 
exhauster  inlet.  On  the  outlet,  the  pressure  to  be  overcome  varies  in  accordance 
with  the  resistance  offered  by  the  apparatus  following  and  the  quantity  of  gas  passing 
at  the  time.  In  the  aggregate,  it  may  vary  between  8  inches  to  10  inches  on  a  small 
country  works  to  as  much  as  50  inches  of  water  on  the  largest  plants,  but  in  average 
cases  it  will  be  accounted  for  somewhat  as  follows  : — 


EXHAUSTING  MACHINERY 


307 


PRESSURE  CONDITIONS  THROUGHOUT  THE  APPARATUS 


Retorts 

Hydraulic  main  . 
Exhauster  inlet  . 
,,         outlet 
Tar  extractor,  outlet  . 
Washers,  outlet  . 
Scrubbers,  outlet 
Purifiers,  outlet  . 
Station  meter,  outlet  . 
Holder,  inlet  and  outlet 


Level-gauge. 

i  inch  to  1  inch  vacuum. 

4  inches  vacuum. 
30  pressure. 

26  Pressure  thrown  by  tar  extractor,  4  inches. 

24 
22 

9 

8-5 

8-5 

30  inches 


washers 

2 

scrubbers 

2 

purifiers 
meter 

13 
0-5 

holder 

8-5 

From  the  above  it  will  be  seen  that  the  forcing  of  the  gas  through  the  dry  puri- 
fication material  and  the  raising  of  the  holder  bell  account  for  the  greatest  portion 
of  the  work  which  the  exhauster  has  to  perform  against  back-pressure.  At  times 
the  physical  condition  of  the  purifying  material  may  give  rise  to  considerably  in- 
creased pressure,  when  the  offending  vessel  must  be  shut  off,  or  a  tier  of  oxide 
"  slipped  "  by  drawing  the  slides  specially  provided  for  this  purpose. 


TYPES  OF  EXHAUSTERS 

In  considering  the  mechanical  details  of  exhausters  it  is  advisable  to  classify 
the  various  types  under  the  following  headings  : — 

(a)  Reciprocating  types. 
(6)  Rotary  types. 

(c)  Steam  jet  types. 

(d)  Turbo-exhausters. 

Reciprocating  machines  operated  on  the  pump  principle  need  be  given  no 
further  notice  owing  to  their  tendency  to  disappear  entirely.  Rotary  exhausters 
of  various  types  are  almost  exclusively  used  at  the  present  day,  whilst  the  most 
recent  development  of  the  same  principle  is  the  turbo-exhauster.  The  first  attempt 
to  construct  a  practicable  rotary  exhauster  was  made  by  Beale  in  1850,  and  this 
machine,  with  important  modifications  and  refinements,  has  served  as  a  model 
for  the  modern  apparatus.  About  the  same  year  G.  Jones  introduced  a  blower 
operating  on  thie  Roots'  principle,  but  for  gasworks  purposes  the  machine  has  not 
gained  much  favour  in  this  country,  although  in  America  it  seems  to  be  preferred. 
Some  years  later  the  Beale  exhauster  was  much  improved  by  Messrs.  Gwynne  & 
Co.,  who  introduced  two  overlapping  blades  instead  of  the  single  one  originally 
employed.  The  Gwyhne-Beale  exhauster  is  shown  in  Fig.  205.  The  blades  pass 
through  slots  cut  in  the  inner  drum,  which  is  revolved  from  the  source  of  power. 
The  extremities  of  the  blades  are  provided  with  steel  cased  pins  which  are  fitted  into 
segments.  The  segments  travel  in  grooves  cast  in  the  end  covers  of  the  drum, 
so  that  when  the  inner  drum  revolves  the  blades  are  drawn  in  and  out,  thus  sucking 
in  the  gas  from  one  port  and  discharging  at  the  second.  The  main  defect  of  this 


308 


MODERN   GASWORKS   PRACTICE 


exhauster  was  the  large 
amoun^  of  friction  produced 
by  the  guiding  segments  run- 
ning at  a  high  speed,  whilst 
the  compound  slide  required 
frequent  renewal.  The 
machine  was,  therefore,  soon 
displaced  by  an  improved 
form,  also  due  to  Beale,  in 
which  the  guiding  segments 
were  eliminated.  The  blades 
in  the  new  type  (Fig.  206) 
were  guided  from  the  centre 
of  the  outer  casing  by  the  use 
of  a  block  running  on  a  cen- 
tral shaft  fixed  in  one  of  the 
end  plates.  The  two  slides 
were  then  cast  in  one  piece, 
and  the  frictional  losses  so 

reduced  as  to  lessen  the  driving  power  required  to  about  two-thirds  of  that  of 
the  original  machine.  A  feature  in  the  machine  is  that  the  outer  casing  is  not 
bored  to  a  true  cylinder,  but  is  oval  in  shape,  this  being  necessary  owing  to  the 
slightly  eccentric  movement  of  the  blades  which  slide  on  the  centre  block. 

MULTIPLE  BLADE  EXHAUSTERS 

The  primary  objection  to  exhausters  of  the  two-blade  type  is  the  irregularity 
of  the  vacuum  they  produce  on  the  inlet  side,  particularly  when  running  at  slower 
speeds.  In  order  to  avoid  such  oscillation  the  exhauster  having  more  than  two 
blades  was  introduced  about  the  year  1879  ;  and  owing  to  the  many  advantages 


FIG.  205. — GWYNNE-BEALE  EXHATJSTER. 


FIG.  206. — IMPROVED  BEALE  EXHAUSTER. 


EXHAUSTING  MACHINERY 


309 


FIG.  207. — 3-BLADE  EXHAUSTER. 


offered  the  multiple  type  is  by  far  the 
most  common  in  use  at  the  present 
time.  Stated  briefly,  the  advantages 
which  the  multiple  machine  possesses 
over  the  two-blade  type  are  as 
follows  : — 

(a)  For  the  same  size  an  in- 
creased capacity  is  obtained,  amount- 
ing to  about  30  per  cent,  with  the 
three-blade  type  and  40  per  cent,  with 
the  four-blade  type,  as  compared  with 
the  two-blade  machine. 

(6)  The  oscillation  is  considerably 
reduced. 

(c)  The   outer  cylinder  is  a  true 
circle,  consequently  no  special  boring 
machinery  is  required. 

(d)  The  whole  machine  is  more  easily  constructed. 

On  the  other  hand,  as  is  often  pointed  out,  the  increase  in  the  number  of  blades 
is  obtained  only  by  reducing  the  extent  of  the  wearing  surfaces,  and  some  engineers 
state  that  the  three  or  four-blade  machines  have  their  disadvantages  in  cases  where 
the  back-pressure  at  the  outlet  is  considerable  and  where  high  speed  is  necessary. 
Typical  examples  of  the  multiple  exhauster  are  shown  in  Figs.  207  and  208. 
The  outer  drum  is  bored  truly  cylindrical,  whilst  the  internal  drum  (which  is  about 
two-thirds  the  diameter  of  the  external  casing)  is  fitted  with  three  or  four  small 
rolls  which  are  slotted  out  to  take  the  blades,  and  oscillate  in  the  bearings  according 

to  the  movement  of  the  blades.  The 
ends  of  the  rolls  project  beyond  the 
width  of  the  inner  drum  and  are  sup- 
ported in  bored  recesses  in  the  end 
covers.  The  blades  are  hinged  on  a 
shaft  which  is  central  with  the  outer 
drum,  and  which  extends  the  whole 
length  of  the  cylinder  and  is  supported 
in  a  deep  boss  on  the  back  cover,  and 
secured  by  a  nut.  To  facilitate  lubri- 
cation this  spindle  is  bored  down  its 
entire  length.  The  driving  shaft  is 
cast  on  to  the  inner  drum  and  pro- 
jects through  a  gland  and  stuffing  box 
in  the  inner  cover.  In  order  to  reduce 
the  losses  by  "  slip  "  the  tips  of  the 
blades  are  fitted  with  T-shaped  strips 
FIG.  208.— WALLER  4-BLADE  EXHAUSTER.  which  are  forced  against  the  inner 


310 


MODERN   GASWORKS   PRACTICE 


periphery  of  the  drum  by 
spiral  springs.  The  construc- 
tion of  these  exhausters  will 
be  readily  seen  by  referring 
to  Figs.  209  and  210. 

The  number  of  blades 
fitted  bears  some  relation  to 
the  capacity  of  the  exhauster  ; 
and,  in  general,  all  machines 
dealing  with  less  than  5,OCO 
cubic  feet  per  hour  are  fitted 
with  two  blades ;  all  above 

FIG.  209. — WALLER  EXHAUSTER  WITH  END-PLATE  REMOVED,     this  capacity  and  up  to  25,000 

cubic  feet  per  hour  are  of  the 

three-blade  type;  whilst  four  blades  are  fitted  for  sizes  larger  than  this. 
The  smallest  rotary  exhausters  made  are  3  inches  internal  diameter  and 
3  inches  long,  but  these  are  seldom  used  for  anything  beyond  adding  air  to 
the  dry  purifiers  or  for  compressing  purposes.  They  are  of  the  two-blade 
type,  running  at  about  500  revolutions  per  minute,  and  having  a  gross  out- 
put of  about  115  cubic  feet  per  hour.  The  largest  exhausters  manufactured, 
which  are  chiefly  employed  on  coke-oven  works,  have  a  capacity  of  about 
450,000  cubic  feet  per  hour,  and  are  4  feet  6  inches  in  diameter.  They  are 
almost  invariably  driven  by  electricity,  as  shown  in  Fig.  211. 

METHODS  OF  DRIVING 
Some  years  ago  it  was  the  common 
practice  to  drive  the  larger  exhausters  by 
means  of  belting,  but  the  method  is  now 
fast  giving  way  to  the  direct-coupled 
system.  The  belt  drive  is  ob j  ectionable  owing 
to  the  possibility  of  the  belt  slipping,  in 
which  case  the  exhauster  may  stop  abruptly, 
on  account  of  friction  between  the  blades 
and  the  case.  The  cost  of  driving  power  is, 
of  course,  the  chief  consideration  in  the  case 
of  the  small  works,  and  as  steam  power  is 
frequently  not  available  in  such  cases,  a  gas 
engine  drive  through  a  countershaft  and 
belting  is  the  only  alternative.  An  advan- 
tage attending  this  method  is  the  possibility 
of  driving  liquor  and  other  pumps  from  the 
same  countershaft.  (A  recommendation  for 
the  use  of  the  exhauster  in  small  works— 
and  one  which  can  scarcely  be  gauged  in 


FIG.  210. — EXHAUSTER,  SHOWING  INNER 
DRUM  PULLED  AWAY  FROM  BLADES. 


311 


terms  of  £  s.  d. — is  that  a  greater  pressure  may  be  maintained  on  the  district 
mains,  thus  the  annual  quantity  of  gas  consumed  may  undergo  augmentation.) 
On  the  larger  and  medium-sized  works,  where  an  ample  supply  of  steam  is  always 
at  hand,  exhausters  are 
frequently  driven  by 
reciprocating  or  turbine 
steam  engines.  Many 
devices  have  been  intro- 
duced with  the  object  of 
ensuring  efficiency  and 
economy.  With  the 
larger  exhausters  it  is 
always  profitable  to  in- 
stal  a  compound  engine, 
owing  to  the  consider- 
able saving  it  effects  in 
steam  consumption.  On 
the  larger  works  a  con- 
densing engine  still 
further  increases  the 
efficiency  of  steam  con- 
sumption. When,  how- 
ever, a  single  cylinder 
engine  is  installed  some 
attention  to  thfe  valve 
setting  is  necessary.  All 
exhauster  engines  may 
be  operated  with  a  com- 
paratively early  "  cut- 
off," and  the  admission 
of  steam  for  the  whole 
length  of  the  stroke 
must  be  looked  upon  as 
unjustifiable  e  x  t  r  a  v  a- 
gance.  In  the  majority 
of  cases  the  "  cut-off  " 
maybe  arranged  at  half- 
stroke,  though  many 
engines  will  be  found 
working  at  three-quarters 
or  seven-eighths.  The 

later  "  cut-off  "  probably  emanates  from  the  fact  that  some  engineers  are  of  the 
opinion  that  closure  at  any  earlier  period  is  conducive  to  unsteady  running ;  but  if 
the  fly-wheel  is  of  sufficient  proportions  this  will  not  be  found  to  be  the  case. 


312  MODERN  GASWORKS   PRACTICE 

'Cases  are  known  where  engines  are  running  at  a  quarter  "  cut-off,"  and  with  no 
undesirable  effect  on  the  "  draw."  When  a  "  cut-off  "  is  used,  however,  a  rather 
larger  engine  is  necessary  ;  and  for  high-pressure  steam  it  is  certainly  advisable  to 
fit  an  expansion  gear,  so  that  a  sharper  and  earlier  effect  may  be  obtained.  With 
very  low-pressure  steam  it  is  essential  to  work  with  admission  during  the  whole 
stroke. 

KUNMING  SPEED 

It  is  not  generally  realized  that  when  regulating  an  exhauster  the  speed  to  be 
considered  is  not  the  actual  number  of  revolutions  performed  by  the  drum  per 
minute,  but  the  peripheral  speed  of  the  tips  of  the  blades.  For  a  given  number  of 
revolutions  per  minute  the  peripheral  speeds  of  (say)  a  6-inch  drum  and  a  4-feet 
diameter  drum  would  be  widely  different,  the  blade  tips  travelling  at  a  greatly 
increased  linear  velocity  in  the  latter  case.  In  both  cases,  however,  the  peripheral 
speeds  should  be  approximately  equal,  and  for  exhausters  of  all  sizes  there  is  very 
nearly  a  constant  peripheral  speed,  which  should  vary  only  between  the  limits  of 
650  and  850  feet  per  minute.  Thus  a  6-inch  exhauster  running  at  350  revolutions 
per  minute  gives  a  peripheral  speed  of  650  feet  per  minute,  and  a  3-foot  machine 
running  at  70  revolutions  per  minute  has  also  a  peripheral  speed  of  about  650  feet 
per  minute. 

GOVERNING  THE  CAPACITY 

There  are  two  standard  methods  of  governing  exhausters : — 

(a)  By  inserting  an  automatically  controlled  by-pass  between  inlet  and  outlet. 

(6)  By  automatically  throttling  the  steam  supply,  or  controlling  the  electric 
current. 

When  a  gas  engine  drive  is  employed  the  first  method  only  is  practicable,  as  the 
speed  of  the  engine  cannot  be  varied  to  any  great  extent  by  the  ordinary  means  of 
governing  employed.  Schemes  for  effecting  this  have  certainly  been  suggested ; 
but,  at  the  most,  the  result  is  only  partial,  and  the  most  convenient  arrangement  is 
to  work  the  engine  in  conjunction  with  a  countershaft  to  which  a  stepped  pulley 
is  fitted. 

The  ordinary  arrangement  of  governing  with  a  by-pass  valve  is  shown  in  Fig. 
212.  The  inlet  and  outlet  of  the  exhauster  are  connected  by  a  short  length  of  pipe 
in  which  an  ordinary  butterfly  valve,  attached  to  a  quadrant  (Fig.  213)  is  inserted. 
The  quadrant  is  then  attached  by  a  chain  and  lever  to  the  bell  of  a  small  gasholder 
which  is  connected  by  a  small  service  pipe  (F)  to  the  inlet  main  of  the  exhauster. 
The  quantity  of  gas  coming  away  from  the  retort  house  varies  to  some  considerable 
extent  at  different  periods  of  the  day.  Accordingly,  the  intensity  of  vacuum  pro- 
duced will  also  vary  in  ratio  to  the  amount  passing  if  the  speed  of  the  exhauster 
is  permitted  to  remain  constant.  In  this  type  of  governing  the  speed  of  the  engine 
is  maintained  fairly  constant,  and  at  a  sufficient  velocity  to  take  the  maximum 
quantity  of  gas  coming  from  the  retorts.  When  the  quantity  passing  along  the 
foul  main  undergoes  reduction  the  vacuum  becomes  momentarily  increased ; 


EXHAUSTING  MACHINERY 

\ 


313 


FIG.  212. — EXHAUSTER  GOVERNING  BY  BY-PASS. 

accordingly,  the  holder  bell  drops  and  operates  through  its  link  motion  to  open 
the  by-pass  valve.  In  this  way  gas  is  sucked  back  from  the  outlet  to  the 
inlet,  and  compensates  for  the  falling  off  in  the  quantity  coming  from  the 
retorts — thus  the  original  vacuum  is  maintained.  In  the  same  way,  as  the 
quantity  of  gas  passing  along  the  foul  main  increases 
the  vacuum  momentarily  decreases,  with  the  result 
that  the  holder  bell  rises  and  closes  down  the  by-pass 
valve  until  the  normal  "  draw  "  is  given.  The  method 
is  certainly  effective,  but  care  is  necessary  to  see  that 
the  exhauster  is  running  at  a  sufficient  speed  to  deal 
with  the  maximum  quantity  of  gas  likely  to  pass  at 
any  time  from  the  retorts,  for  the  governor  cannot 

increase    the    speed   of   the    engine   should    this   be   in- 

FIG.  213. — QUADRANT  AND 
sufficient   at   any   period.      Fig.  214   shows  a    complete  VALVE. 


314 


MODERN   GASWORKS   PRACTICE 


FIG.  214. — COMPLETE  EXHAUSTER  INSTALLATION  SUITABLE  FOR  A  SMALL  WORKS. 


gas-driven  exhausting  plant  with  by-pass  governor  suitable  for  a  small  works. 
There  is  little  doubt  that,  wThen  the  size  of  the  plant  permits,  exhauster  govern- 
ing can  be  most  effectively  carried  out  by  varying  the  speed  of  the  engine  employed 
for  driving.  This  is  simply  effected  by  employing  a  gasholder  bell  the  interior  of 
which  is  in  communication  with  the  vacuum  side  of  the  exhauster.  Buoyancy  is- 
imparted  by  means  of  air-floats  placed  at  the  base  of  the  bell,  whilst  the  upward 
or  downward  movement  of  the  bell  is  conveyed  by  link  motion  to  the  throttle  valve 
of  the  engine.  Briefly  explained,  the  operation  of  the  governor  is  as  follows  : — 
Should  the  quantity  of  gas  passing  to  the  inlet  of  the  exhauster  decrease,  then  the 


EXHAUSTING   MACHINERY 


315 


intensity  of  vacuum  in  the  inlet  main  will  increase.  But  the  service  pipe  (A,  Fig. 
215)  transmits  this  increase  of  vacuum  to  the  interior  of  the  bell,  which,  accordingly, 
is  pulled  downwards.  The  downward  movement  of  the  bell  then  operates  through 
the  link-motion  to  close  the  throttle  valve  (H)  slightly  so  that  the  speed  of  the  engine 
is  reduced  in  accordance  with  the  amount  of  gas  coming  along.  In  the  same  way,, 
when  the  quantity  of  gas  increases,  the  vacuum  on  the  inlet  falls,  with  the  result 
that  the  bell  ascends  and  opens  the  steam  throttle  to  the  required  extent.  By 
adjusting  the  cock  placed  at  R,  on  the  top  of  the  bell,  the  rate  at  which  the  bell  rises 
and  falls  may  be  regulated.  In  some  instances  steadiness  of  movement  is  assured 
by  introducing  the  principle  of  the  "  dash-pot." 


1 

1 

1 

1  L^.»_ 
1 

1 
1 
1 
1 
j  1 

STEAM  E/vorMf 

I 

^^^ 

1 

FIG.  215. — EXHAUSTER  GOVERNING  BY  THROTTLE. 

In  laying  down  exhauster  installations  it  is  frequently  arranged  that  both 
by-pass  and  throttle  governors  shall  be  provided.  On  large  works  where  a  number 
of  exhauster  units  are  employed,  there  is  no  necessity  for  a  by-pass  governor,  for, 
according  to  the  make,  exhauster  sets  are  started  up  or  shut  off  and  the  whole  of 
the  governing  can  be  done  by  steam  regulation.  On  small  and  medium-sized  works, 
however,  where  only  duplicate  machines  are  in  use,  a  single  exhauster  has  probably 
to  deal  with  the  maximum  winter  and  minimum  summer  make.  In  this  case  the 
exhauster  is  usually  installed  to  allow  room  for  future  extension  ;  consequently,  with- 
out the  by-pass  governor  it  would  have  to  run  at  an  inconveniently  low  speed  when 

J    i  o  •/  IT 

dealing  with  the  minimum  make.     In  such  cases  it  is  preferable,  therefore,  to  supply 
a  by-pass  governor,  which  is  adjusted  from  time  to  time  according  to  the  season, 


316 


MODERN   GASWORKS   PRACTICE 


whilst  the  throttle  governor  controls  the  speed  of  the  engine  according  to  the  varying 
makes  during  the  24  hours. 

THE  LUBRICATION  OF  EXHAUSTERS 

The  lubrication  of  the  exhauster  is  a  point  requiring  very  careful  attention, 
for  endless  trouble  may  follow  the  use  of  unsuitable  oils.  For  most  purposes  the 
best  lubricant  is  a  mixture  of  refined  creosote  and  mineral  oil — one  part  of  the  former 
to  three  of  the  latter.  A  heavy  oil  should  always  be  used,  also  an  oil  that  will  act 
as  a  solvent  to  the  tar,  such  as  a  good  mineral  oil,  rather  than  a  vegetable  oil  which 
will  thicken  with  the  tar.  The  temperature  of  the  gas,  the  quantity  of  suspended 
tar,  and  whether  the  gas  is  clean  or  foul  are  all  important  factors  from  the  point 
of  view  of  lubrication ;  and  experience  is,  perhaps,  the  most  reliable  guide.  When 
the  exhausters  are  preceded  by  tar  extractors  it  will  be  found  preferable  to  use 
an  ordinary  engine-oil  of  good  quality.  The  tar  vesicles  present  in  the  gas  possess 
very  important  properties  in  relation  to  the  lubrication  of  the  exhauster,  and  it  is 
important  to  ensure  that  the  necessary  fluidity  of  the  tar  is  maintained.  Dr.  Car- 
penter has  emphasized  the  value  of  the  tar  present  by  showing  that,  when  the  ex- 
hausters are  placed  prior  to  the  condensers  in  sequence,  not  a  drop  of  lubricating 
oil  is  necessary. 

Special  apparatus  for  the  lubrication  of  exhausters  is  now  nearly  always  em- 
ployed. The  forms  most  generally  made  use  of  are  : — 

(a)  Ordinary  self-contained  drip-feed. 

(6)  Pressure  system,  embodying  the  use  of  a  reservoir  from  which  the  oil  is 
expelled  by  the  pressure  of  gas  at  the  outlet  of  the  exhauster. 

(c)  Mechanical  appliances,  such  as  miniature  pumps  driven  by  gearing  or  belting 
from  the  exhauster  shaft. 

One  of  the  last-named  devices  is  shown  in  Fig.  216.  It  consists  of  an  oil  pump 
which  is  driven  by  gearing  from  the  main  shaft  of  the  exhauster.  Above  the  pump 
is  an  oil  reservoir  from  which  the  oil  is  sucked,  and  pumped  under  pressure  to  the 
various  parts  requiring  lubrication.  The  pump  may  be  fitted  with  a  single  plunger, 


FIG.  216. — MECHANICAL  PUMP  LUBRICATOR  FOR  EXHAUSTER. 


EXHAUSTING  MACHINERY  317 

or  may  be  of  the  multiple  type  according  to  the  number  of  points  at  which  lubri- 
cation is  desired.  It  should  be  noted  that  whatever  form  of  lubrication  is  made 
use  of  it  is  essential  that  the  oil  be  filtered  before  use. 

The  several  points  at  which  an  exhauster  should  be  lubricated  depend  largely 
upon  the  type  of  the  machine.  Taking,  however,  as  an  instance  one  of  the  three 
or  four  blade  types  such  as  Waller's  (Fig.  208),  it  will  be  seen  that  the  inner  drum 
is  supported  and  rotates  in  recessed  covers,  therefore  lubrication  is  required  at  these- 
points.  The  hinges  upon  which  the  blades  are  carried  upon  the  central  spindle  are 
lubricated  by  means  of  an  oil  hole  provided  by  boring  through  the  whole  length 
of  the  spindle,  oil  being  forced  through  this  duct  by  an  automatic  or  hand  pump. 
In  the  case  of  the  old  pattern  two-blade  Beale  exhauster  the  inner  drum  is  sup- 
ported by  the  shaft,  which  is  carried  in  outside  bearings  ;  these  require  lubrication,, 
as  do  the  segments  which  rotate  in  grooves  in  the  covers.  The  latest  pattern  Beale 
machine  is  provided  with  a  recessed  back  cover  which  requires  lubrication,  the 
driving  shaft  is  supported  by  an  outer  bearing  which  must  also  be  lubricated,  whilst 
the  steel  spindle  supporting  the  centre  block  upon  which  the  blades  rotate  is  pro- 
vided with  a  hole  for  injecting  oil.  When  possible,  a  continuous  flow  of  oil,  as 
given  by  one  of  the  mechanical  lubricators,  should  always  be  arranged  for,  this- 
being  very  much  more  effective  than  an  intermittent  supply.  The  distribution 
must,  moreover,  be  uniform,  as  a  dry  portion  where  contact  occurs  quickly  results1, 
in  heating  and  subsequent  erosion  of  the  surfaces. 

PKECATJTIONS  AGAINST  STOPPAGE 

Owing  to  the  seizure  of  a  bearing,  the  slipping  of  a  belt,  the  burning  out  of  a 
fuse,  or  some  other  unlooked-for  cause,  an  exhauster  is  liable  to  pull-up  at  short 
notice.  This,  of  course,  should  not  occur  if  the  machine  is  properly  attended 
to  ;  but,  nevertheless,  it  is  an  emergency  which  must  always  be  provided  for.  In. 
addition  to  duplicate  plant  some  means  should  be  provided  for  guarding  against 
the  undue  pressure  which  would  otherwise  be  thrown  upon  the  retorts  and  the 
apparatus  between  them  and  the  exhauster.  A  usual  method  is  to  insert  in  a  by- 
pass pipe  connecting  inlet  and  outlet  a  safety  flap- valve  such  as  that  shown  in  Fig. 
217.  In  the  ordinary  wTay  the  outlet  pressure  holds  the  valve  against  its  seatingsr 
but  should  the  exhauster  stop  the  inlet  pressure  will,  after  a  time,  exceed  that  on 
the  outlet,  so  that  the  valve  is  forced  open,  giving  a  free  way  for  the  gas.  It  will 
be  realized,  however,  that  only  temporary  relief  is  afforded  before  the  pressure  of 
the  whole  apparatus  will  be  thrown  on  the  retorts.  The  flap  valves  are  usually 
fitted  with  a  handle,  as  shown,  so  that  they  may  occasionally  be  jarred  in  order  to 
ensure  that  sticking  will  not  occur. 

On  the  rare  occasions  when  the  exhausting  plant  breaks  down  it  is  unreason- 
able to  expect  that  no  loss  of  gas  whatever  need  take  place,  and  the  most  simple 
and  safe  means  of  providing  against  such  a  contingency  is  that  of  inserting  a  safety 
seal  in  the  main  leading  from  the  retort-house  to  the  exhauster.  This  seal  can  be 
regulated  to  some  definite  depth — usually  about  6  to  8  inches — thus  only  a  small 
pressure  will  be  exerted  upon  the  apparatus  before  the  gas  blows  away.  The  seal 


318 


MODERN   GASWORKS   PRACTICE 


FIG.  217. — SAFETY  FLAP- VALVE. 


should  be  arranged  at  some  point  in  the  open  where  there  will  be  no  chance  of 
the  escaping  gas  igniting.  In  making  use  of  a  seal  of  this  kind  it  is  necessary 
to  ensure  that  the  blow-off  pipe  is  sealed  to  a  greater  depth  than  the  maximum 
possible  "  draw  "  at  this  point ;  otherwise  air  will  be  sucked  in. 


CALCULATION  OF  CAPACITY 

Figures  given  by  makers  for  the  capacity  of  exhausters  denote  the  amount  of 
gas  passed  at  normal  temperature.  The  exhauster  has,  however,  to  deal  with  an 
amount  of  gas  varying  from  5  to  10  per  cent,  in  excess  of  this  rated  quantity.  In 
addition,  "  slip  "  past  the  blades  is  a  fairly  considerable  item,  for  which  further  allow- 
ance has  to  be  made.  The  amount  of  "  slip  "  occurring  is  entirely  dependent  upon 
the  difference  of  pressure  between  the  inlet  and  outlet  of  the  exhauster,  and  is  inde- 
pendent of  speed.  But  it  may  be  taken  as  a  general  rule  that  as  speed  increases 
the  proportional  <(  slip "  undergoes  reduction.  In  calculating  the  capacity  of 
exhausters  it  is  customary  to  make  an  allowance  of  15  to  20  per  cent,  for  "  slip," 
according  to  the  size  of  the  machine. 

The  calculation  of  the  capacity  of  an  exhauster  is  not  so  simple  as  might  at 
first  sight  be  supposed.  Considering  an  ordinary  four-blade  machine  it  must  be 
remembered  that  the  capacity  is  not  the  whole  space  swept  out  by  each  blade  per 
revolution.  The  amount  of  gas  carried  forward  by  each  pair  of  blades  is  the 


EXHAUSTING   MACHINERY 


319 


FIG.  218. 


greatest  volume  which  exists  at  any  time  be- 
tween the  two  blades.  By  reference  to  Fig.  218 
it  can  be  seen  that  at  each  revolution  a  volume 
of  gas  having  a  cross-sectional  area  equal  to  the 
shaded  portion  of  the  figure  is  carried  from  inlet 
to  outlet  by  each  pair  of  blades ;  and  in  one 
revolution  of  the  exhauster  this  volume  is  taken 
in  and  delivered  four  times.  When  considering 
a  two  or  three-blade  machine  the  volume  be- 
tween the  blades  (for  a  given  size)  is,  of 
course,  greater  than  with  the  four-blade  ;  but 
then  it  is  only  displaced  two  or  three  times 
in  one  revolution  instead  of  four  times. 

For  a  four-blade  exhauster  the  following 
method  of  calculating  capacity  may  be  used, 
but  it  cannot  be  said  to  be  closely  accurate 
when  very  large  or  very  small  sizes  are  under  consideration. 

Let     D  =  the  inside  diameter  of  outer  drum  in  feet. 
L  =  length  of  drum  in  feet. 
N  =  Revolutions  made  per  minute. 
Q  =  Cubic  feet  of  gas  passed  per  hour. 

Then  Q^  65D2LN. 

This  gives  the  gross  capacity,  from  which  20  per  cent,  should  be  deducted  for 
"slip." 

The  capacity  of  modern  exhausters  has  been  increased  to  a  certain  extent  by 
the  introduction  of  relief -port  passages  which  enable  the  blades  to  continue  drawing 
for  a  longer  period  and  provide  a  greater  area  for  the  issuing  gas.  It  is  questionable, 
however,  whether  these  passages  are  perfectly  satisfactory. 

DRIVING  POWER  REQUIRED 

The  motive  power  is  the  largest  item  in  the  running  costs  of  exhausters.  As 
regards  the  horse-power  required  for  any  one  installation  it  is  almost  impossible  to 
lay  down  a  hard  and  fast  rule,  for  so  much  depends  upon  the  conditions  under  which 
the  plant  is  working.  A  mere  table  of  powers  is,  therefore,  apt  to  be  misleading. 
The  power  varies  considerably ;  for  instance,  an  exhauster  made  to  pass  100,000 
cubic  feet  per  hour  at  its  standard  speed  would  have  about  65  to  70  per  cent,  effi- 
ciency if  working  against  30  inches  to  60  inches  back- pressure.  If,  however,  the 
machine  was  put  to  work  to  pass  25,000  cubic  feet  per  hour,  the  power  required 
could  not  be  taken  in  the  same  ratio  to  the  gas  passed,  for  the  amount  of  power 
lost  would  bear  a  much  larger  ratio  to  the  gas  passed  than  in  the  first  case.  Hence 
the  efficiency  of  the  machine  when  dealing  with  small  quantities  will  be  much  lower. 
There  is  no  fixed  rule  as  to  what  to  allow  for  efficiency  in  such  cases,  and  much 
depends  on  the  type  of  machine  under  consideration.  In  practice,  it  is  usual  to 
treat  each  case  on  its  merits,  to  suit  the  prevailing  conditions.  Some  idea  of  the 


320 


MODERN   GASWORKS   PRACTICE 


probable  horse-power  required  may,  however,  be  obtained  from  the  following  table, 
compiled  by  E.  B.  Donkin: — 

HORSE-POWER  REQUIRED  TO  PASS  GAS  AGAINST  VARIOUS  PRESSURES. 
(Friction  of  Exhauster  neglected.) 


Capacity  per. 
Hour. 

Cubic  feet. 

TOTAL  PBESSUEE  OF  GAS  IN  INCHES  OF  WATER. 

6 

9 

12 

15 

18 

20 

24 

30 

36 

40 

50 

5,000 

0-08 

0-12 

0-16 

0-19 

0-24 

0-26 

0-31 

0-39 

0-47 

0-53 

0-66 

10,000 

0-16 

0-24 

0-31 

0-39 

0-47 

0-53 

0-63 

0-79 

0-95 

1-05 

1-31 

15,000 

0-24 

0-36 

0-47 

0-58 

0-71 

0-79      0-94 

1-18 

1-42 

1-58 

1-97 

20,000 

0-31 

0-47 

0-63 

0-79 

0-95 

1-05  |    1-26 

1-58 

1-90 

2-10 

2-63 

25,000 

0-39 

0-59 

0-79 

0-98 

1-18 

1-31 

1-58 

1-97 

2-37 

2-63 

3-29 

'    30,000 

0-48 

0-71 

0-94 

1-18 

1-42 

1-57 

1-89 

2-36 

2-83 

3-15 

3-94 

40,000 

0-62 

0-94 

1-26 

1-58 

1-90 

2-10 

2-52 

3-15 

3-78 

4-21 

5-26 

50,000 

0-79 

1-18 

1-58 

1-97 

2-36 

2-63 

3-15 

3-94 

4-73 

5-25 

6-57 

60,000 

0-94 

141 

1-89 

2-36 

2-84 

3-15 

3-79 

4-73 

5-67 

6-30 

7-89 

80,000 

1-24 

1-84 

2-52 

3-16 

3-80 

4-20 

5-04 

6-30 

7-56 

8-42 

10-5 

100,000 

1-58 

2-37 

3-16 

3-94 

4-73 

5-26      6-31 

7-89 

9-47 

10-5 

13-15 

150,000 

2-37 

3-54      4-72       5-90 

7-09 

7-87      9-46 

11-8 

14-2 

15-8 

19-7 

200,000 

3-16 

4-74  |  6-32       7-88 

9-46 

10-5      12-6 

15-8 

18-9 

21-0 

26-3 

250,000 

3-95 

5-92 

7-90 

9-85 

11-8 

13-1 

15-7 

19-7 

23-6 

26-2 

32.9 

300,000 

4-74 

7-11 

9-48 

11-8 

14-1 

15-7 

18-9 

23-6 

28-4 

31-5 

39-4 

The  additional  allowance  for  friction  will  vary  from  40  to  ICO  per  cent,  of  the 
figures  given  by  the  above  table.  As  an  illustration  of  this  item,  the  following 
examples  are  given  : — 

PERCENTAGE  TO  ADD  TO  POWERS  GIVEN  IN  ABOVE  TABLE  IN  ORDER  TO  FIND  HORSE-POWER  TO 

DRIVE  EXHAUSTER. 


Capacity  per  Hour. 

Back-pressure. 

Add  to  previous  Power. 

10,000  cubic  feet      .     .     .     .  : 

12  inches 

100  per  cent. 

20,000      „        „        .     .     .     . 

18       „ 

90 

50,000      „        „        .      .     .     . 

24       „ 

70 

100,000      „        „        .      .     .     . 

30       „ 

50 

200,000      „        „        .      . 

36       „ 

45 

300,000      „        „        .... 

50       „ 

40 

Thus  for  an  exhauster  passing  100,000  cubic  feet  against  30  inches  back  pressure 
an  engine  of  about  12  b.h.p.  would  suffice,  although  it  is  always  as  well  to 
allow  an  additional  margin  of  25  per  cent.,  bringing  the  total  brake  horse-power 
up  to  15. 


EXHAUSTING  MACHINERY 


321 


STEAM  JET  EXHAUSTERS 

Steam  jet 'exhausters 
working  on  the  injector 
principle  are  compara- 
tively rare  features  of 
the  modern  gasworks  in 
this  country,  although 
they  continue  to  find  a 
certain  amount  of  favour 
on  the  Continent.  A 
notable  instance  of  the 
employment  of  this  type 
o  f  exhauster  is  the 
Gloucester  gasworks, 
where  apparatus  of  the 
kind  has  been  in  use  since 
1877,  when  the  works 
were,  built.  First  intro- 
duced by  Cleland,  the 
steam  jet  was  afterwards 
improved  by  Korting, 
and  is  seen  in  Fig.  219. 
Steam  at  about  50  Ib. 
pressure  is  projected 
through  a  series  of  trun- 
cated cones  gradually 
increasing  in  size.  The 
gas  is  drawn  in  through 
spaces  at  the  nozzles  of 
the  cones  and  is  carried 
forward  by  the  pressure 
of  the  steam.  Care 
should  be  taken  to  ensure 
that  dry  steam  only  is 
used,  and  this  is  after- 
wards extracted  from  the 
gas  by  condensing  appar- 
atus. The  capacity  of 
the  exhauster  may  be 
regulated  within  com- 
paratively wide  limits  by 
an  adjustable  needle- 
valve  at  the  steam  inlet,  and  by  a  moveable  sleeve  which  opens  or  closes  the  gas 


inlet 


322 


MODERN   GASWORKS   PRACTICE 


ports.  The  chief  merits  of  this  type  of  exhauster  are  that  pulsation  is  entirely  avoided, 
and  there  are  no  constantly  moving  mechanical  parts  to  give  rise  to  wear  and  tear.  On 
the  other  hand,  there  is  the  expense  of  providing  additional  condensers,  whilst  steam 
•consumption  is  high.  The  jet  may  be  interposed  at  various  points  in  the  series 
of  apparatus.  In  some  cases  it  is  preferred  to  place  it  in  the  foul  main,  almost  imme- 
diately after  the  hydraulic  main,  others  make  use  of  it  after  the  condensers,  but 
at  Gloucester  it  comes  just  prior  to  the  dry  purification  plant.  Some  advocates 
of  the  steam-jet  exhauster  have  said  that  it  gives  rise  to  a  direct  increase  in  illumin- 
ating power  equal  to  as  much  as  three-quarters  of  a  candle.  It  is  difficult,  how- 
ever, to  see  en  what  grounds  such  a  gain  in  quality  could  take  place.  At  the  Glou- 
cester works  the  expenditure  on  wear  and  tear  over  a  period  of  about  30  years 
amounted  to  £5. 

TURBO-EXHAUSTERS 

The  chief  drawback  to  the  ordinary  rotary  exhauster  is  the  necessity  for  a 
considerable  amount  of  rubbing  contact  and  the  large  frictional  area  brought  into 
play,  with  a  consequent  reduction  in  efficiency.  In  recent  years  these  difficulties 


FIG.  220. — TWO-STAGE  WALLER  TURBO-EXHAUSTER. 


EXHAUSTING  MACHINERY 


323 


FIG.  221. — THREE-STAGE  WALLER  EXHAUSTER. 


have  been  overcome  by  the  introduction  of  the  high-speed  machine  working  on 
the  fan  principle  and  providing  large  clearances.  A  further  advantage  offered 
by  the  centrifugal  fan  exhauster  is  its  greater  volumetric  capacity  in  proportion 
to  the  floor-space  occupied. 

In  order  to  deal  with  pressures  commonly  met  with  on  gasworks,  it  is  generally 
necessary  to  build  these  machines  with  two  or  more  Impellers  which  rotate  on  a 
common  axis  but  in  separate  cells.  By  means  of  suitable  passages  the  gas  is  passed 
from  cell  to  cell  in  series  until  it  is  discharged  from  the  machine  at  the  requisite 
pressure,  this  pressure  being  the  sum  of  the  amounts  by  which  it  is  increased  at 
each  stage.  The  intensity  of  this  increase  of  pressure  per  stage  is  dependent  upon 
the  diameter  and  speed  of  the  impellers,  and  also  upon  the  specific  gravity  of  the 
gas  at  the  time  of  its  being  passed  through  the  machine.  Constructional  difficulties 
inherent  to  this  type  of  exhauster  have,  up  to  the  present,  restricted  its  use  to  works 
with  a  large  output.  So  far  it  has  been  found  impracticable  to  build  them  in  sizes 
which  will  deal  with  the  requirements  of  small  or  medium-sized  works  with  the 
efficiency  and  reliability  which  characterize  the  ordinary  rotary  type. 

As  might  be  expected  the  several  designs  now  to  be  had  differ  considerably, 
but  many  are  based  on  the  principles  of  Professor  Rateau,  who  has  devoted  con- 
siderable time  to  the  study  of  the  subject.  Figs.  220  and  221  show  the  Waller 
type  of  turbo-exhauster,  the  two-stage  machine  being  driven  by  steam  turbine, 


324 


MODERN   GASWORKS   PRACTICE 


FIG.  222. — BRITISH  THOMSON-HOUSTON  TURBO-EXHAUSTER. 


and  the  three- stage  by  elec- 
trical motor.  The  impellers 
of  these  machines  are  built  up 
from  steel  plates  bolted  to  a 
cast-iron  centre,  whilst  the 
spindles  are  of  steel,  running 
at  the  driving  end  in  white 
metal  bearings  with  oil-ring 
lubrication,  the  outer  ends 
running  in  ball  bearings.  A 
ball  bearing  is  also  provided 
at  this  end  to  take  up  the 
axial  thrust  of  the  spindle  due 
to  the  pressure  of  the  gas  on 
the  impellers.  The  exhauster 
and  prime  mover  are  mounted 
on  a  cast-iron  box  section. 
The  machine  shown  in  Fig.  220  is  driven  by  a  de  Laval  turbine  running  at  4,000 
revolutions  per  minute,  and  will  pass  50,000  cubic  feet  of  gas  per  hour  against  a 
pressure  of  30  inches.  The  larger  machine  (Fig.  221)  is  rated  for  a  capacity  of 
170,000  cubic  feet  per  hour  against  a  pressure  of  42  inches.  Owing  to  the  high  speed 
at  which  turbo-exhausters  have  to  run,  they  are  particularly  suited  for  being  driven 
direct  by  electric  motor  or  steam  turbine  without  the  employment  of  intermediate 
gearing.  Another  type  of  fan  exhauster  is  shown  in  Fig.  222.  This  is  the  British 
Thomson-Houston  machine  driven  by  a  Curtis  impulse-type  steam  turbine  through 
a  flexible  coupling.  The  exhauster  is  of  the  two-stage  type,  and  is  capable  of  dealing 
with  500,000  cubic  feet  of  gas  per  hour  against  a  pressure  of  40  inches.  In  this 
case  the  impellers  are  placed  back  to  back 
in  order  to  eliminate  end-thrust.  Fig.  223 
shows  one  of  the  impellers,  which  are  solid 
steel  castings,  the  blades  and  hub  being 
in  one  piece,  with  the  exception  of  the  inlet 
ends  which,  being  twisted  to  allow  free 
entry  of  the  gas,  are  mounted  on  a  small 
extension  hub.  On  leaving  the  impeller 
the  gas  passes  through  a  series  of  exit 
guide  blades,  which  convert  the  velocity 
head  into  pressure  head.  As  regards  initial 
cost  this  is,  on  an  average,  about  50  per  1P^" 
cent,  less  than  that  of  an  ordinary  rotary 
installation  of  the  same  capacity.  Owing 
to  the  high  rate  of  speed,  pulsation  with 
this  type  of  exhauster  is  almost  entirely 
eliminated.  FIG.  223. — EXHAUSTER  IMPELLER. 


EXHAUSTING  MACHINERY  325 

EXHAUSTERS   PRIOR  TO   CONDENSERS 

The  position  of  the  exhauster  is  entirely  arbitrary.  In  almost  all  cases,  how- 
ever, it  will  be  found  in  sequence  between  the  condensing  and  washing  plant.  Some 
engineers  prefer  to  place  the  machine  either  before  the  condensers  (so  that  con- 
densing takes  place  under  pressure),  or  after  the  washers  (so  that  both  condensers 
and  washers  are  under  a  vacuum).  The  practice  of  condensing  under  pressure 
has  assumed  some  importance,  and  finds  a  stout  advocate  in  Dr.  Carpenter.  The 
problem  of  the  most  effective  means  of  lubricating  an  exhauster  is  always  a  vexed 
one,  and  is  said  to  be  more  troublesome  when  the  light  oil  tars  have  been  removed 
from  the  gas  in  the  process  of  condensation.  When,  however,  the  exhauster  is 
placed  prior  to  the  condensers,  so  that  it  is  operated  at  a  temperature  of  about 
140°  Fahr.,  no  lubricant  is  necessary,  the  condition  of  the  gas  being  sufficiently 
oily  to  ensure  smooth  running  of  the  machine.  By  placing  the  exhauster  at  a  point 
nearer  to  the  hydraulic  main  a  shorter  length  of  main  under  vacuum  is  assured, 
so  that  there  is  less  probability  of  the  intake  of  air  through  defective  joints.  At 
the  present  day,  however,  the  latter  consideration  has  lost  a  good  deal  of  its  former 
significance,  owing  to  the  reduction  in  standards  of  illuminating  power,  and  the 
fact  that  lime  purification  is  obsolescent.  The  disadvantage  attached  to  exhausting 
hot  gas  is  that  owing  to  its  increased  temperature  the  bulk  of  the  gas  is  augmented, 
hence  additional  exhauster  capacity  is  necessary.  If  the  average  temperature 
of  the  gas  is  about  140°  Fahr.,  the  additional  capacity  required  (compared  with 
the  ordinary  practice  of  exhausting  at  70°  Fahr.)  will  amount  to  about  15  per  cent. 


CHAPTER   XIV 
THE  PRELIMINARY  PURIFICATION  OF  COAL  GAS 

THE  purification  of  coal  gas  commences  directly  the  gas  reaches  the  hydraulic  main, 
by  which  time  it  has  undergone  a  considerable  drop  in  temperature.  At  this  point 
some  of  the  impurities  will  be  washed  from  the  gas  by  the  deposition  of  a  portion  of 
the  aqueous  vapour  and  by  its  passage  through  the  hydraulic  seal.  The  impurities 
in  crude  coal  gas  at  this  stage  may  be  summarized  as  follows  : — 

(1)  Suspended  tarry  matter  and  condensible  hydrocarbons. 

(2)  Ammonia. 

(3)  Sulphuretted  hydrogen. 

(4)  Carbon  disulphide  and  other  sulphur  compounds. 

(5)  Carbonic  acid,  by  which  term  carbon  dioxide  (C02)    is    generally  known 

on  gasworks. 

(6)  Hydrocyanic  acid,  usually  spoken  of  as  cyanogen. 

(7)  Naphthalene. 

Of  these,  the  last  three  can  scarcely  be  classified  as  impurities,  and  there  is 
no  statutory  obligation  to  remove  either  these  or  No.  4.  Whilst  it  is  in  all  cases 
to  the  engineer's  own  interest  to  reduce  the  naphthalene  content  to  such  a  quantity 
as  can  be  carried  by  the  gas  without  deposition,  the  removal  of  cyanogen  and  sulphur 
compounds  is  (owing  to  the  very  small  quantities  in  which  they  are  present)  not 
so  imperative,  and  is  only  carried  out  in  rare  instances.  Carbon  dioxide,  though 
invariably  classified  as  such,  is  in  no  sense  an  impurity,  but  may  be  looked  upon 
as  an  inert  diluent  having  a  certain  deteriorating  influence  upon  the  illuminating 
and  heating  values  of  the  gas  (see  page  393). 

In  the  preliminary  purification  of  coal  gas  by  wet  methods  it  is  the  removal  of  a 
portion  of  the  sulphuretted  hydrogen  and  carbon  dioxide  with  which  we  are  chiefly 
concerned.  At  the  same  time  the  last  traces  of  suspended  tar  must  be  eliminated. 
In  order  to  understand  the  principles  upon  which  the  process  is  based,  it  is  necessary 
to  consider  the  nature  of  the  various  substances  present  in  the  crude  gas,  i.e.  whether 
they  are  acid  or  alkaline.  Thus  we  have-: — 

Ammonia — alkaline . 

Carbon  dioxide — acidic  properties. 

Sulphuretted  hydrogen — acidic  properties. 

Hydrocyanic  acid — acid. 

In  the  first  instance,  advantage  is  taken  of  the  powerful  affinity  possessed  for 
ammonia  by  water  which,  at  normal  temperature  and  pressure,  is  capable  of  absorbing 
about  780  times  its  own  volume  of  ammonia  gas.  Thus,  treatment  of  the  crude 
gas  with  water,  in  special  vessels  known  as  washers  and  scrubbers,  affords  a  ready 


326 


THE  PRELIMINARY  PURIFICATION  OF  COAL  GAS     327 

means  of  removing  this  impurity.  Water  also  possesses  some  affinity  for  carbon 
dioxide  and  sulphuretted  hydrogen,  but  its  capacity  in  this  direction  is  but  slight,  one 
volume  absorbing  about  three  and  a  quarter  volumes  of  sulphuretted  hydrogen,  or 
one  volume  of  carbon  dioxide.  Carbon  disulphide  gas  is  also  soluble  in  water,  but 
to  a  very  small  extent,  amounting  to  about  one-thousandth  part  of  the  volume  of 
water.  Advantage  is  taken  of  the  fact  that  the  ammonia  solution  formed,  being 
of  an  alkaline  nature,  is  capable  of  ready  reaction  with  the  acid  impurities  in  the  gas.. 
Thus  carbon  dioxide,  the  strongest  acid  present,  and  sulphuretted  hydrogen,  are 
absorbed,  with  the  formation  of  certain  definite  salts  which  are  themselves  soluble 
in  the  water.  In  the  ordinary  sense  ammoniacal  liquor  consists  of  water  containing 
in  solution  a  certain  proportion  of  these  salts. 

It  is  necessary  to  emphasize  that  the  quantity  of  ammonia  which  water  can 
absorb  is  not  entirely  dependent  upon  temperature,  for  solubility  also  varies  in 
direct  proportion  to  the  pressure  of  the  ammonia  gas.  If  pure  ammonia  gas  i«  in 
contact  with  water  at  normal  temperature  and  pressure  (60°Fahr.  and  30  inches  Bar.) 
then  the  water  is  capable  of  absorbing  an  amount  equal  to  780  times  its  own  volume. 
In  crude  gas,  however,  the  proportion  of  ammonia  to  the  whole  volume  is  trifling, 
hence  the  pressure  it  will  exert  is  only  in  proportion  to  the  extent  of  its  presence. 
For  instance,  if  ammonia  is  present  to  the  extent  of  one  per  cent,  of  the  whole,  then 
the  pressure  it  exerts  will  amount  to  merely  0-01  atmospheres,  at  wrhich  pressure 
very  little  affinity  exists  between  it  and  the  water.  It  is  this  fact  which  explains- 
the  necessity  for  using  a  comparatively  large  quantity  of  water  per  ton  of  coal  car- 
bonized (see  page  356),  and  shows  why  the  question  of  time  contact  is  one  which  must 
be  considered  in  the  design  of  washers  and  scrubbers. 

Ammonia  in  crude  coal  gas  is  usually  found  to  the  extent  of  about  1  -5  per  cent, 
by  volume,  and  of  this  amount  from  a  third  to  one- half  will  have  been  washed  out 
by  the  aqueous  vapour  and  have  been  deposited  by  the  time  the  gas  has  reached 
the  outlet  of  the  condensers.  In  this  respect  the  figures  of  Hunt,  who  found  the 
distribution  of  ammonia  as  follows,  are  of  interest : — 

Ammonia  removed  by  condensation    .          .          .          .     42  •  7  per  cent,  of  total. 
„  „  first  scrubber  .         .         .          .     43-3     „       „  ,, 

„  „  second       „       .          ..        .          .     14-0     ,,       „  „ 

When  gas  containing  sulphuretted  hydrogen  and  carbon  dioxide  comes  in  contact 
with  a  solution  of  ammonia,  the  amount  of  the  acid  gases  absorbed  may  be  sufficient 
to  give  rise  to  a  neutral  or  normal  salt,  or  absorption  may  continue  until  the  ammonia 
solution  contains  about  20  per  cent,  more  of  the  acids  than  is  sufficient  to  give  the 
neutral  salts.  Hence,  both  acid  and  normal  salts  result  as  follows  : — 

Ammonia  and  Carbon  Dioxide — 

(1)  2NH4OH  +  C02  =  (NH4)2C03  (ammonium  carbonate)   +  H20.     Normal. 

(2)  NH4OH  +  CO 2  =  NH4,HC03  (ammonium  bicarbonate).     Acid. 

Ammonia  and  Sulphuretted  Hydrogen — 

(1)  2NH4OH  +  SH2  =  (NH4)2S    (ammonium    sulphide)  +  2H20.    NormaL 

(2)  NH4OH  +  SH2  =  NH4,HS  (ammonium  hydrosulphide)  +  H20.    Acid. 


328  MODERN  GASWORKS   PRACTICE 

Actually,  the  acid  salts  are  not  formed  direct,  as  shown  above,  but  from  further 
absorption  of  acid  gases  by  the  normal  solutions,  as  follows  :  — 
(NH4)2,C03  +  H20  +  C02  =  2NH4,HC03. 
S  +  SH2=2NH4HS. 


THE  COMPOSITION  OF  GAS  LIQUOR 

The  liquor  deposited  in  the  hydraulic  main  and  condensers  is  generally  char- 
acterized as  "  virgin  liquor,"  which  signifies  that  the  water  in  which  the  salts  are 
dissolved  emanates  from  the  coal  and  not  from  external  sources.  In  the  ordinary 
way  the  yield  of  virgin  liquor  varies  from  10  to  14  gallons  per  ton  of  coal  carbonized. 
The  hydraulic  main  liquor  differs  considerably  from  that  obtained  in  the  washing 
plant,  chiefly  owing  to  the  fact  that  the  temperature  at  this  point  (about  140°  Fahr.) 
•renders  many  of  the  compounds  which  are  found  at  the  lower  temperatures  unstable. 
'Thus  the  salts  formed  as  in  the  above  reactions,  i.e.  the  carbonates  and  sulphides, 
are  present  in  only  small  quantities,  there  is  little  free  ammonia  in  comparison  with 
the  amount  in  the  scrubber  liquor,  and  fixed  ammonia  salts  may  predominate. 

Ammonia  in  gas  liquor  may  be  combined  in  two  distinct  ways,  first  as  easily 
decomposable  compounds  such  as  carbonates  and  sulphides  and,  secondly,  as  more 
stable  compounds  which  will  not  undergo  decomposition  by  heating,  but  which 
require  the  addition  of  a  caustic  alkali  to  liberate  the  ammonia  from  them.  In  the 
former  case,  the  ammonia  is  combined  with  the  weaker  acidic  gases  C02  and  SH2 
and  is  known  as  "  free  "  ammonia.  In  the  latter  case  it  is  combined  with  stronger 
acids,  such  as  hydrochloric  and  sulphuric,  and  is  then  called  "  fixed  "  ammonia. 
'.The  "  fixed  "  ammonium  salts  in  gas  liquor  are  the  outcome  of  the  combination 
•of  ammonia  with  the  minor  impurities  in  the  crude  gas  and  are  derived  to  some 
•extent  from  oxidation.  In  general,  the  final  mixture  of  gas  liquor  obtained  in  the 
storage  well  contains  from  75  to  80  per  cent,  of  the  "  free  "  salts  and  from  20  to  25 
jper  cent,  of  "  fixed  "  salts,  the  probable  constituents  being  as  follows  :  — 

THE  COMPOSITION  OF  GAS  LIQUOR 

Water  containing  in  solution  :  — 
Ammonium  carbonate 

bicarbonate 


carbamate 

sulphide 

hydrosulphide 


"  Free  "  ammonia 

75  to  80  per  cent,  of 

total  ammonia. 


„  cyanide 

„  polysulphide 

,,  chloride              ,. 

,,  sulphocyanide    j 

„  sulphite                                    "  Fixed  "  ammonia 

„  thiosulphate       I                 20  to  25  per  cent,  of 

„  sulphate                                       total  ammonia. 

„  .       ferrocyanide       I 

„  acetate                / 

"Also  phenols,  amines  and  other  nitrogenous  bodies. 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     329 

It  does  not  follow  that  gas  liquor  will  contain  every  one  of  the  above  salts  ;  in 
fact,  some  of  those  included  are  only  met  with  on  rare  occasions.  Ammonium 
carbamate,  CO(ONH4)NH2  is  deposited  as  a  white  solid  when  C02  and  ammonia 
meet.  It  is  easily  soluble  in  water,  but  is  probably  present  in  only  minute  quantities 
in  gas  liquor,  for,  when  dissolved,  it  is  soon  converted  into  carbonate.  As  regards 
the  "  fixed  "  salts,  these  are  largely  accounted  for  by  ammonium  chloride,  which 
owes  its  presence  to  the  common  salt  (sodium  chloride)  present  in  the  original  coal. 
The  amount  of  salt  varies  considerably  according  to  the  class  of  coal  used,  the  maxi- 
mum proportion  in  the  coal  being  about  0-25  per  cent.  Ammonium  chloride  is  a 
particularly  unwelcome  compound,  for,  in  addition  to  its  deleterious  effects  on  the 
fireclay  of  the  retorts,1  it  has — in  the  gaseous  state — a  marked  corrosive  action 
on  the  steelwork  of  the  hydraulic  main,  etc.  When  deposited  in  the  solid  state  it 
may  give  rise  to  considerable  trouble,  due  to  the  stoppage  of  pipes,  and  in  some 
cases  special  means  have  been  introduced  for  dealing  with  it.2 

Ammonium  cyanide  is  present  only  in  traces,  and  is  very  generally  absent 
altogether.  The  ferrocyanide  is  also  of  rare  occurrence,  so  much  so  that,  during 
an  examination  of  various  liquors  extending  over  a  period  of  five  years,  conducted 
by  the  chief  inspector  under  the  Alkali  Act,  it  was  only  identified  with  certainty 
on  one  occasion.  Ammoniacal  liquor  is  considerably  affected  by  oxidation,  so  that 
its  ultimate  constituents  are  influenced  in  some  degree  by  the  amount  of  oxygen 
present  in  the  gas.  A  process  of  gradual  oxidation  from  one  compound  to  another 
takes  place,  the  final  salts  obtained  depending  upon  the  extent  to  which  the  oxidation 
has  occurred.  Ammonium  polysulphide  and  thiosulphate  are  the  first  products 
of  oxidation,  these  being  formed  from  ammonium  sulphide,  although,  in  the  case 
of  the  former,  the  action  is  more  mechanical  than  chemical.  Oxidation,  then, 
proceeds  progressively,'  so  that  in  turn  the  thiosulphate,  sulphite  and  lastly,  sulphate 
are  formed,  whilst  in  certain  cases  free  sulphur  may  be  deposited.  The  sulphite 
is  usually  only  present  in  faint  traces,  which  is  probably  accounted  for  by  the  fact 
that  solutions  of  polysulphide  and  sulphite  react  to  form  sulphide  and  thiosulphate  : 
(NH4)2S2  +  (NH4)2S03  =  (NH4)2S  +  (NH4)2S208.  At  the  same  time  ammonum 
thiosulphate  may  be  formed  by  reaction  between  the  sulphite  and  sulphide  : — 
4(NH4-)2S03  +  2(NH4)2S  =  3(NH4)2S203  +  6NH3  +  3H20.  Lunge  asserts  that  am- 
monium polysulphide  cannot  exist  in  ordinary  ammoniacal  liquors,  since  it  reacts 
with  sulphites  and  cyanides.  At  one  time  there  was  some'  doubt  as  to  whether  gas 
liquor  contained  any  actual  free  ammonia  (i.e.  dissolved  NH3),  but  investigators  such 
as  Gerlach  and  Tieftrunck  have  shown  this  to  be  the  case.  Owing  to  the  fact  that 
acetylene  is  of  a  slightly  acid  nature,  ammonium  acetate  (CH3COONH4)  may  in  some 
cases  be  found  in  gas  liquor.  When  liquor  is  distilled  with  an  alkali  (lime)  for  the 
manufacture  of  sulphate  of  ammonia,  the  final  traces  of  ammonia  are  seldom  expelled, 
so  that  some  slight  loss,  amounting,  under  best  conditions,  to  about  0-1  per  cent., 
is  inevitable.  This  is  in  some  measure  due  to  the  fact  that  certain  of  the  ammonia- 
bearing  compounds  (such  as  the  amine  bodies)  require  rather  more  energetic  treat- 
ment to  bring  about  complete  decomposition. 

1  See  Chapter  VI,  page  148,  2  See  Chapter  VII,  page  176. 


330  MODERN   GASWORKS   PRACTICE 

From  the  foregoing  remarks,  it  will  be  gathered  that  the  final   composition 
of  ammoniacal  liquor  depends  upon — 
(a)  The  class  of  coal  carbonized. 
(6)  The  amount  of  salt  in  the  coal. 

(c)  The  temperature  of  distillation. 

(d)  The  means  employed  for  separating  liquor  and  gas. 

(e)  The  temperature  to  which  the  liquor  is  subjected. 

(/)  The  amount  of  oxygen  in  the  gas,  the  amount  of  air  drawn  in  on  the  inlet 
of  the  exhauster,  and  the  extent  to  which  the  liquor  is  exposed  to  the  atmosphere. 

Item  (d)  is  one  which  is  frequently  overlooked,  and  may  have  some  considerable 
influence  on  the  amount  of  ammonia  present  in  the  crude  gas.  For  instance,  when 
tar  towers  are  in  use  the  ammonia  in  the  gas  at  the  outlet  of  the  condensers  is  fre- 
quently lower  than  200  grains  per  100  cubic  feet,  in  contrast  with  about  3CO  grains 
when  the  system  of  a  separate  draw-off  to  each  hydraulic  is  installed.  The  reason 
would  appear  to  be  that  in  the  case  of  tar  towers  the  maintenance  of  the  seal  is 
ensured  by  running  liquor  into  the  tower  alone.  When  weir  valves  or  other  individual 
means  are  in  use  the  liquor  is  usually  laid  on  to  each  hydraulic,  and  by  giving  rise 
to  splashing  sets  free  ammonia,  which  is  accordingly  carried  forward  by  the  gas. 
In  the  ordinary  way  the  hydraulic  main  liquor  contains  about  50  per  cent,  of  its 
ammonia  in  the  fixed  form,  chloride  and  sulphocyanide  predominating.  At  the 
present  day,  however,  it  is  a  growing  practice  to  circulate  the  liquor  repeatedly  through 
the  hydraulics,  and  in  such  cases  the  fixed  content  will  be  considerably  increased, 
so  that  it  may  amount  to  as  much  as  80  per  cent,  of  the  ammonia  present. 

The  proportion  of  ammonia  contained  in  gas  liquor  is  in  reality  quite  small. 

In  normal  cases  the  total  ammonia  varies  from  1-5  to  2  per  cent.,  being  appor- 
tioned as  follows  : — 

Free  ammonia         .          .          .          .          .          .          .          .     1-2  to  1-6  per  cent. 

Fixed  ammonia       ........     0-3  to  0-4     „       „ 

As  regards  C02  and  SH2  the  following  figures  may  be  taken  as  illustrating 
average  conditions  : — 

CO2  in  gas  liquor  .          .          .          .          .          .          .     1-3  to  2      per  cent. 

SH2  „  ....  .     0-1  to  0-6     „       „ 

Sulphur    „  .  .     0-5  to  0-7     „       „ 

It  is  difficult  to  lay  down  any  hard  and  fast  figures  in  connexion  with  the  manner 
in  which  the  ammonia  is  distributed,  but  in  general  it  will  be  accounted  for  somewhat 
as  follows.  The  manner  in  which  the  sulphur  is  combined  is  also  given. 

DISTRIBUTION  OF  AMMONIA  IN  GAS  LIQUOR. 

,  ,,      |  Ammonium  sulphides         .....       6  per  cent,  of  total  ammonia. 

(  „  carbonates      .          ....  74  „  „  „ 

„  chloride  .....  15  „  „  ,, 

"  T?'     A"  J  "  sulphocyanide          ....       1-75  „  „  .. 

„  thiosulphate,  sulphite,  etc.  3  „  „  ,, 

„  sulphate          .....  0*25  „  „  ,,. 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     331 

DISTRIBUTION  OF  SULPHUR  IN  GAS  LIQUOR. 

Sulphur  combined  with  free  ammonia  as  sulphides  .          .  .     55  to  75  per  cent,  of  total. 

„  „  „     fixed  ammonia  as  sulphocyanide .  .      15  to  25         „  ,, 

„  „  „         „  „         as  sulphate.          .  1  to     5         „  „ 

„  „  •  „         „  „         as  thiosulphate     .  ,       5  to  15         „  „ 

„  „          in  other  forms  (poly sulphide,  etc.)        .  1  to     5         „  „  • 

The  ammonia  present  in  coal  gas  has  provided  the  gas  engineer  with  a  simple 
means  of  eliminating  the  chief  impurities  in  the  gas,  but  there  is  a  limit  to  the  extent 
of  the  purification  which  can  be  carried  out  through  its  agency,  for  the  amount  of 
the  alkali  present  in  crude  gas  is  only  in  the  neighbourhood  of  1-5  per  cent,  by  volume. 
Of  this,  about  one-fourth  to  one-fifth  is  combined  as  fixed  salts,  thus  the  surplus 
available  for  the  removal  of  sulphuretted  hydrogen  and  carbon  dioxide  amounts  to 
about  1-2  per  cent.  Together  the  SH2  and  C02  in  the  crude  gas  (excluding  any  C02 
which  may  be  drawn  in  from  the  furnace)  total  about  2|-  per  cent,  by  volume,  thus 
the  ammonia  available  is  theoretically  sufficient  for  removing  only  about  one-half 
of  these  impurities.  At  the  outlet  of  the  condensers  the  impurities  in  the  gas  will 
be  present  in  approximately  the  following  proportions  : — 

IMPURITIES  IN  GAS  AT  OUTLET  OF  CONDENSERS, 

Grains  per  100  Fer  cent,  by 

cubic  feet.  volume  (average). 

Ammonia.          .          ....          .          .          .     200  to  300  .  .."        0-75 

Sulphuretted  hydrogen        .          .          .  .     600  to  900  ..          1-0 

Carbon   dioxide          .          .       ....          .         ,          .     900  to  1,400          ..          1-5 

Sulphur  compounds   .          .    '  •"  ,          .          .          .       35  to  45 
Hydrocyanic  acid       .         .          .          .          .          .       60  to  80 

Naphthalene      .      '    .         ,          .          .          '.  .  •      .       20  to  25 

THE  ABSORPTION  or  CARBON  BISULPHIDE 

As  previously  pointed  out,  water  absorbs  only  about  one-thousandth  part  of 
its  own  volume  of  carbon  disulphide  ;  and,  in  the  usual  way,  from  2  to  4  grains  of 
this  impurity  are  removed  from  the  gas  during  its  passage  through  the  washers 
and  scrubbers.  The  reduction  of  carbon  disulphide  by  treatment  with  liquor  has 
for  long  been  a  subject  of  investigation,  and  the  extent  to  which  the  compound  may 
be  absorbed,  also  the  actual  chemical  manner  in  which  its  removal  is  effected, 
have  given  rise  to  a  good  deal  of  discussion.  In  the  first  place,  it  is  by  no  means 
certain  (as  is  so  often  stated)  that  CS2  is  directly  absorbed  by  ammonium  sulphide 
with  the  formation  of  ammonium  thio carbonate,  according  to  the  equation  — 
(NH4)  2S  +  OS  2  =  (NH4)  2CS  3  Tilden  states  that  an  interaction  takes  place  between 
carbon  disulphide  and  ammonia  whereby  a  sulphocyanide  and  sulphide  are  formed, 
but  heat  is  necessary  for  the  reaction— 4NH3  +  CS2  =  NH4CNS  +  (NH4)2S.  The 
same  authority  states  that  combination  of  the  two  gases  may  give  rise  to  ammonium 
sulphocyanide  and  thiocarbonate— 4NH  3  +  2CS  2  =  NH4CNS  +  (NH4)  2CS  3.  The 
actual  manner  in  which  the  CS2  is  removed  is,  however,  not  at  all  clear,  and  whilst  it 
appears  to  unite  with  ammonium  sulphide  on  the  lines  of  the  first  of  the  reactions 
shown  above  it  seems  essential  that  polysulphides  or  free  sulphur  should  be  present ; 
for  the  two  substances  do  not  combine  when  in  the  pure  state.  The  carbon  dioxide 


332 


MODERN   GASWORKS   PRACTICE 


in  the  gas,  moreover,  would  have  detrimental  effects  from  the  point  of  view  of  CS2 
removal ;  for  it  tends  to  dissociate  ammonium  thiocarbonate  and  to  set  free  the 
sulphur  compound.  Some  express  the  opinion  that  ammonium  polysulphide  is 
alone  the  agent  by  means  of  which  the  CS2  is  removed. 

Although  all  attempts  at  the  reduction  of  sulphur  compounds  by  treatment 
with  liquor  have  been  attended  with  somewhat  erratic  results,  there  seems  little 
doubt  that  some  appreciable  reduction  may  be  effected  by  dealing  with  the  gas  whilst 
in  its  hot  state.  One  method  of  treatment  is  thoroughly  to  wash  the  gas  with  hot 
liquor  in  the  hydraulic  main,  the  liquor  being  circulated  and  recirculated  so  that 
only  the  surplus  flows  away.  Lunge  states  that  the  liquor  from  the  hydraulic  main 
is  especially  suited  for  wet  purification,  for  it  contains  some  considerable  quantities 
of  free  ammonia  (i.e.  NH3)  owing  to  the  far-going  dissociation  of  the  "  free  "  salts — 
•carbonate  and  sulphide.  It  is  probable,  therefore,  that  some  absorption  of  CS2  may 
take  place  owing  to  the  presence  of  uncombined  ammonia  in  the  liquor,  and  after 
the  manner  of  Tilden's  equations  already  referred  to.  No  great  reliance  can,  however, 
be  placed  in  the  method.  It  has,  in  consequence,  not  been  generally  undertaken 
on  gasworks. 

So  far  as  the  difference  of  constitution  of  the  liquor  from  the  hydraulic  main  and 
of  the  final  product  obtained  in  the  storage  well  is  concerned,  Meyer  and  Hempel 
have  given  the  following  interesting  table  : — 


Liquor  from  Storage  Well. 

Liquor  from  Hydraulic 

Main. 

Total  ammonia        .... 

1200-6  grains  per  gallon 

405-7  grains  per  ga 

Ion 

"Free"        „           .... 

984-5       „ 

204-1       „ 

, 

"  Fixed  "      „ 

216-1       „ 

201-6       „ 

' 

Ammonium  carbonate  . 

2468      grains  per  gallon 

332     grains  per  ga 

lion 

sulphide     . 

193 

51 

, 

thiosulphate    . 

86 

30 

, 

sulphite      . 

Traces 

Nil 

sulphate    . 

16          „         „        „ 

16 

i 

chloride 

517 

505 

,     • 

sulphocyanide 

127         „        „        „ 

70         „        „       , 

t 

ferrocyanide    . 

6-2       „ 

2-3      „ 

t 

cyanide 

8-3       „ 

24       „         „        , 

, 

Uncombined  ammonia. 

7-4      „        „       „ 

73-0      „        „       , 

METHODS -OF  OPERATING  WET  PURIFICATION  PLANT 

The  most  efficient  manner  of  operating  washers  and  scrubbers  is  to  ensure  that 
til**  gas  on  first  entering  the  apparatus  is  treated  with  the  strongest  liquor  obtainable, 
whilst  in  each  subsequent  vessel  the  liquor  circulated  becomes  gradually  weaker 
until,  in  the  final  scrubber,  clean  water  is  employed.  Where  circumstances  permit 
it  is  preferable  that  the  decarbonating  vessel  be  worked  with  hydraulic  main  liquor, 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     333 

as  this  contains  a  large  proportion  of  uncombined  ammonia,  available  for  the  re- 
moval of  CO  2  and  SH2.  Considerable  care  should  be  taken  in  order  to  prevent 
the  passage  forward  of  tar  to  the  ammonia  washers.  At  the  inlet  to  the  washing 
plant  this  impurity  should  be  reduced  to  as  low  as  2  grains  per  100  cubic  feet  of  gas. 
Davidson  has  said  that  the  crude  gas  in  the  hydraulic  main  contains  as  much  as  8,000 
grains  of  tar  per  100  cubic  feet. 

The  effect  of  submitting  the  gas  to  clean  water  in  the  final  scrubber  is  to  remove 
practically  the  last  traces  of  ammonia  from  the  gas,  whilst  the  water  is  converted 
into  a  weak  liquor  (from  1  to  2  oz.  strength),  which,  mixed  with  that  flowing  from 
the  condensers  and  hydraulic  mains,  is  passed  down  the  previous  portions  of  apparatus 
and  finally  worked  up  to  the  desired  strength.  Herring  says  that  the  weak  liquor 
has  a  slightly  greater  affinity  for  the  sulphuretted  hydrogen,  but  as  its  strength  in- 
creases the  carbon  dioxide  exerts  its  superior  affinity,  actively  combines  with  the  free 
ammonia,  and  breaks  up  some  of  the  already  formed  sulphide,  giving,  instead, 
ammonium  carbonate.  Thus  in  certain  of  the  washing  vessels  evolution  of  sulphuretted 
hydrogen  may  occur. 

As  regards  the  amount  of  water  (other  than  that  formed  from  the  distillation 
of  the  coal)  which  is  necessary  in  order  to  effect  the  wet  purification  of  gas,  the  author 
finds  that  with  Durham  coal  the  flow  through  the  final  scrubber  amounts  to  from 
10  to  13  gallons  per  ton  of  coal  carbonized.  With  this  quantity  the  ammonia  in  the 
outlet  gas  is  reduced  to  0-5  grains  per  100  cubic  feet.  Some  years  ago  it  was  con- 
sidered that  the  water  required  for  complete  removal  of  ammonia  should  be  3  gallons 
per  ton  of  coal  used  ;  but  much  must  depend  upon  the  nature  of  the  coal,  the  systems 
of  carbonization  and  condensation,  and  the  type  of  scrubber  in  use. 


WASHING  AND   SCRUBBING  APPARATUS 

The  arrangement  of  the  wet  purification  plant  conforms  to  no  regular  rules, 
so  that  the  apparatus  and  the  method  of  working  it  vary  considerably,  in  accordance 
with  the  tastes  of  the  engineer.  Formerly,  the  removal  of  ammonia  was  effected 
by  the  use  of  no  other  power  than  the  pressure  of  the  gas  itself  ;  but,  recently,  mechan- 
ical devices,  necessitating  the  use  of  external  driving  power,  have  come  into  very 
general  favour.  The  latter  apparatus  is  commonly  known  as  the  washer- scrubber, 
owing  to  its  ability — due  to  increased  efficiency — to  perform  the  greater  portion  of 
the  work  of  these  two  vessels. 

Washing  plant  may  be  taken  to  embrace  those  portions  of  the  apparatus  in 
which  the  gas  is  actually  caused  to  bubble  through  seals  or  to  pass  through  weirs  of 
liquor.  In  scrubbing  plant,  on  the  other  hand,  the  gas  comes  in  contact  with  a 
wetted  surface  of  coke,  boards,  or  other  suitable  material.  In  the  design  of  the 
washer,  the  depth  of  the  seals  employed,  or  the  resistance  offered  (and,  accordingly, 
the  effectiveness  of  the  machine  for  removing  ammonia)  must  be  balanced  against 
the  back-pressure  thrown,  and  in  no  case  should  the  latter  exceed  3  inches  for  a 
single  machine.  Washers  are  invariably  operated  with  liquor  of  the  maximum 
strength,  whereas  in  the  scrubbers,  liquor  of  a  weaker  quality  is  circulated. 


334 


MODERN   GASWORKS   PRACTICE 


To-day,  the  washer  introducing  the  principle  of  wire-drawing  and  bubbling 
has  come  into  very  general  use,  for  not  only  is  such  apparatus  efficient  from  the  point 
of  view  of  the  removal  of  the  gaseous  impurities,  but  it  provides  an  admirable  means 
of  eliminating  tar  where  this  may  have  travelled  forward  to  the  wet  plant.  There 
are  numerous  types  of  this  style  of  washer,  but  probably  the  most  noteworthy  is  that 
designed  by  the  late  Sir  George  Livesey,  and  employed  extensively  throughout 


FIG.  224. — THE  LIVESEY  WASHER. 


the  world.  The  apparatus  is  shown  in  Fig.  224.  It  consists  of  a  rectangular  cast- 
iron  outer  case,  the  upper  portion  of  which  forms  an  inlet  chamber.  To  the  lower 
flanges  of  the  inlet  chamber  is  fastened  a  series  of  wrought-iron  pear-shaped  tubes, 
an  enlarged  section  of  which  is  shown  in  Fig.  225.  It  will  be  noticed  that  whereas 
the  space  between  these  tubes  is  in  communication  with  the  inlet  chamber,  the 
interior  of  the  tubes  is  connected  with  the  outlet  chamber.  Thus  the  gas  has  free 
access  to  the  intermediate  spaces,  passes  downwards  through  them,  and  depresses 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     335 

the  liquid  until  it  (the  gas)  finds  an  outlet  through  the  perforations  in  the  bent  plate 
and  thence  upwards  into  the  space  above  the  plate,  whence  it  travels  to  the  outlet 
chamber.  The  bubbles  of  gas  in  passing  through  the  liquor  into  the  tube  space 
convert  the  surface  into  a  foam,  thus  the  most  thorough  contact  of  gas  and  liquor 
is  assured.  In  order  to  prevent  the  gas  passing  direct  from  the  inlet  to  the  outlet 
chamber  the  ends  of  the  intermediate  spaces  are  securely  closed  up.  The  perforations 
in  the  tubes  are  usually  one-twentieth  of  an  inch  in  diameter,  and  so  placed  that  there 
are  about  thirty  to  the  square  inch.  The  washer  will  be  found  to  work  most  effectively 
when  the  depth  of  liquor  is  such  that  it  rises  to  an  inch  above  the  top  of  the  pear- 
shaped  plates,  in  which  case  3  inches  of  pressure  is  thrown. 


FIG.  225. — LIVESEY  WASHER,  DETAIL  OF  PERFORATED  PLATES. 


There  are  now  many  washers  in  use  which  are  operated  on  the  bubbling  and 
wire-drawing  principle  ;  and  from  the  point  of  view  of  tar  extraction  efficiency  the 
type  is  probably  not  to  be  excelled.  Cockey's  washer  is  shown  in  Fig.  226.  It  con- 
sists of  a  cast-iron  vessel  divided  off  by  horizontal  partitions  into  three  or  more  cham- 
bers. The  gas  entering  at  the  base  travels  upwards  through  a  vertical  pipe  to  the 
top  of  which  is  fitted  a  hood.  The  gas  meets  the  hood  and  is  then  deflected  down- 
wards through  four  openings  in  the  horizontal  plate  and  passes  through  the  liquor. 
It  then  travels  past  several  serrated  edges  which  are  sealed  in  liquor,  and  afterwards 
finds  its  way  to  the  next  chamber.  The  liquor  flows  from  the  top  chamber  down- 
wards ;  and  the  depth  of  the  seals  may  be  regulated  as  desired. 

Dempster's  washer  is  shown  in  Fig.  227.  It  is  composed  of  a  number  of  cast- 
iron  trays  placed  one  above  the  other,  the  trays  having  a  number  of  narrow  openings, 
with  raised  edges.  These  openings  are  covered  with  hocds  having  serrated  edges, 


336 


MODERN  GASWORKS   PRACTICE 


and  each  tray  contains  liquor  in  which  the  serrations  of  these  hoods  are  sealed. 
The  weaker  liquor  enters  at  the  top  and  flows  round  the  hoods,  as  shown  in  the 


Liquor  Inlet 


2"  Sludge  Cock 


Adjustable  Seal 

and 
Overflow  Valves. 


Diagrammattic     / 
Only,  to  Complete 

Overflows  not 
Shown  in  Section 


2"  Tube 


2 "Sludge  Cocks 


To  Tar  Well 


FIG.  226. — COCKEY'S  WASHER. 


sectional  plan,  thence  overflows  to  the  section  below,  and  finally  is  drawn  of?  at  the 
base  of  the  vessel.     The  gas  enters  at  the  bottom  and  passes  upwards  through  the 


openings  in  the  bottom 
tray  and  through  the 
liquor  sealed  serrations 
of  the  hoods  until  it 
passes  to  the  outlet  at 
the  top. 

A  washer  hailing  from 
America  is  known  as 
the  "  Multiple  "  and  is 
shown  in  Fig.  228.  It  is 
designed  on  lines  very 
similar  to  the  Livesey 
type,  horizontal  inverted 
U-section  troughs  being 
used  for  breaking  up  the 
gas.  To  the  lower  edges 
of  each  U-trough  three 
perforated  plates,  set  out 
at  a  wide  angle,  are  at- 
tached. The  plates  are 
set  one  above  the  other, 
but  are  so  arranged  that 
the  distance  they  project 
decreases  from  the  top- 
most downward.  The 
perforations  in  these 
plates  decrease  in  dia- 
meter and  increase  in 
size  from  the  bottom 
upwards,  whilst  their 
edges  are  serrated. 

The     principle      of 
Walker's  washer  is  shown 


SIDE  ELEVATION. 


^^-^^Jplp^ 


o          o o          o          o         o          o          o          o 


FIG.  228.— THE  "  MULTIPLE 

WASHER. 


SECTION  ON  LINE  AB. 

FIG.  227. — DEMPSTER'S  WASHER. 

in  Fig.  229.  The  gas  from  the  inlet  pipe  enters 
a  central  chamber,  branching  away  from  which 
are  a  number  of  longitudinal  troughs,  open  at  the 
bottom  but  closed  at  the  far  end.  The  level  of 
the  liquor  in  the  cast-iron  external  shell  is  such 
that  the  lower  ends  of  the  troughs  are  sealed, 


MODERN   GASWORKS   PRACTICE 

and  whilst  the  bottom  edges  are  perforated  there  are  a  number  of  narrow  slots 
.in  the  side  of  the  troughs  through  wThich  the  bulk  of  the  gas  passes.     In  general, 
the  washer  forms  a  distinct  piece  of  apparatus ;   but,  if  desired,  it  may  be  fitted 
an  the  base  of  a  scrubber,  as  seen  in  Fig.  241  (page  350). 

In. some  cases  the  functions  of  tar-extracting,  washing  and  scrubbing  are  merged 
into  one  vessel,  known  as  a  purifying  machine.  In  the  Walker  apparatus  (Fig.  230) 
the  gas  is  first  treated  in  the  lower  portion  of  the  vessel,  which  contains  a  washer 
-similar  to  that  shown  in  Fig.  229.  It  then  travels  upwards  to  the  next  compartment. 


FIG.  229. — WALKER'S  WASHEE. 


"where  it  conies  in  contact  with  strong  liquor  distributed  over  devices  containing 
wetted  boards.  The  gas  then  travels  through  a  number  of  superimposed*  tiers  of 
.such  boards  and  is  taken  off  at  the  top  of  the  machine.  A  vertical  shaft  passes 
through  the  centre  of  each  of  the  boxes  containing  the  boards,  the  ends  of  the  shaft 
being  connected  to  rocking  levers  carried  from  pivots  on  the  top  of  the  machine.  The 
rocking  levers  are  operated  by  a  small  engine  placed  at  ground  level,  and  by  means 
of  these  levers  the  boxes  are  raised  and  lowered  about  every  ten  seconds.  The  boards 
contained  in  the  boxes  are,  in  this  way,  frequently  immersed  in  the  liquor  contained 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     339 


in  their  respective 
compartments,  and 
are  then  exposed  in 
their  wet  condition  to 
the  crude  gas.  Effec- 
tive contact  with  a 
large  area  of  wetted 
surface  is  thus  ensured. 
Clean  water  is  ad- 
mitted to  the  top  of 
the  machine  at  the 
rate  of  10  gallons  per 
ton  of  coal  carbonized, 
and  flows  out  at  the 
base  as  a  liquor  of 
from  16  to  22  oz. 
strength.  The  back- 
pressure thrown  by 
the  apparatus  is  ex- 
tr  em  ely  small, 
amounting  to  little 
more  than  1  inch  of 
water. 

MECHANICAL  WASHEK- 
SCKUBBERS 


Plant  of  this  de- 
scription has  been 
introduced  with  a  view 
to  combining  the  func- 
tions of  the  washers 
and  scrubbers.  On 
the  majority  of  the 

larger  works  some  apparatus  of  the  kind  is  now  to  be  found.  The  increased  efficiency 
of  ammonia  extraction  obtained  is  largely  dependent  upon  the  large  area  of  freshly 
wetted  surface  with  which  the  gas  is  brought  in  contact,  also  the  "  breaking-up  "  effect 
of  the  mechanically  operated  portions.  The  primary  objection  to  machines  of  this 
type  is  the  necessity  for  employing  motive  power,  whilst  the  introduction  of  run- 
ning parts  accounts  for  some  expenditure  on  wear  and  tear.  At  the  same  time,  the 
capacity  of  the  machines  for  dealing  with  a  definite  quantity  of  gas  is  considerably 
less  than  that  necessary  with  the  ordinary  type  of  washing  and  scrubbing  plant ; 
thus,  when  a  large  stream  of  gas  is  to  be  treated,  substantial  saving  in  capital  out- 
lay will  be  effected  by  the  employment  of  the  washer- scrubber.  There  are  several 


FIG.  230. — WALKER'S  PURIFYING  MACHINE. 


340 


MODERN   GASWORKS   PRACTICE 


types  of  washer-scrubber  now  in  use,  but  in  many  cases  a  strong  resemblance  is 
shown.  Essentially,  the  machines  consist  of  a  series  of  cylindrical  bays,  made 
from  cast-iron,  and  bolted  together  so  as  to  form  a  number  of  compartments.  A 
rotating  shaft  carrying  some  form  of  agitating  gear  runs  through  the  centre  of  the 
cylinder.  The  crude  gas  entering  at  one  end  passes  out  at  the  further  end  of  the 
cylinder  deprived  of  the  greater  portion  of  its  ammonia,  while  clean  water  (flow- 
ing in  at  the  opposite  end  to  the  gas)  travels  from  bay  to  bay,  being  converted  into 
a  liquor  of  gradually  increasing  strength.  In  the  most  ef  ective  machines,  clean 
water  running  into  the  final  bay  will  be  worked  up  to  a  liquor  of  about  12  oz.  strength 
by  the  time  it  reaches  the  opposite  end  of  the  cylinder. 


FlG.    231. — KlRKHAM,    HULETT    AND    CHANDLER'S    "STANDARD"    WASHER-SCRUBBER. 


Washer-scrubbers  may  be  classified  into  two  distinct  groups  : — 

(a)  Horizontal  types. 

(6)  Vertical  centrifugal  types. 

Type  (a)  was  introduced  many  years  ago  by  Paddon,  and  although  it  is  still 
very  much  in  evidence  on  gasworks,  there  is  some  tendency  for  the  more  effective 
centrifugal  type  to  take  its  place.  Of  type  (a)  the  original  machine  of  Kirkham, 
Hulett  and  Chandler  (Fig.  231)  is,  perhaps,  the  best  known.  In  its  latest  and  im- 
proved form  it  consists  of  a  number  of  concentric  cast-iron  rings  bolted  together 
and  divided  into  separate  compartments  by  means  of  circular  division  plates  having 
openings  in  the  centre  to  permit  of  the  passage  of  the  gas.  The  machine  is  con- 
structed in  two  sections  with  intermediate  bearings  at  the  centre,  whilst  a  connecting 
main  from  section  to  section  is  provided  for  the  passage  of  the  gas.  In  the  original 
machine  the  central  shaft  was  carried  on  bearings  inside  the  washing  chambers, 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     341 

which  rendered  the  bearings  extremely  difficult  of  access,  and  frequently  resulted 
in  the  fracture  of  the  shaft.  The  washing  appliance  consists  of  bundles  of  corru- 
gated wrought-iron  sheets,  the  corrugations  of  alternate  sheets  crossing  one  another 
diagonally.  The  bundles  (Fig.  232)  are  attached  together  so  as  to  form  a  complete 
circle,  and  are  fixed  to  the  central  shaft  by  means  of  double  collars.  The  collars 
are  made  of  such  a  size  as  to  obstruct  the  direct  passage  of  the  gas  from  bay  to  bay 
and  to  cause  it  to  take  a  circuitous  path  in  contact  with  the  wetted  bundles.  In 
order  to  preclude  still  further  the  possibility  of  "  slip  "  a  special  arrangement  of 
lead  rings  is  fitted  so  as  to  bear  upon  the  collar  and  completely  close  any  gas  way 


FIG.  232. — CORRUGATED-IRON  BUNDLE  FOR  "STANDARD"  MACHINE. 

except  through  the  bundles.  The  arrangement  is  clearly  seen  in  Fig.  232.  The 
liquor  flows  from  bay  to  bay  by  means  of  the  external  sloping  pipes  shown,  its  usual 
depth  being  rather  less  than  one-third  of  the  diameter  of  the  machine.  When  the 
machine  is  used  for  cyanide  extraction  the  corrugated  iron  bundles  are  replaced  by 
a  somewhat  similar  pattern  made  from  wood. 

The  Whessoe  washer-scrubber  (Fig.  233)  is  very  similar  in  construction  to  that 
described  above,  and  is,  in  fact,  worked  on  the  same  lines  as  the  Kirkham  and 
Chandler  machine.  Wooden  bundles  are  used,  and  the  machine  is  divided  into  four 
sections  and  driven  from  the  centre  of  the  shaft  instead  of  from  one  end. 


342 


MODERN   GASWORKS   PRACTICE 


contain  several  compartments,  all  of  which 


Holmes'  washer-scrubber  is 
now  made  in  two  sections,  as 
shown  in  Fig.  234,  and  is  so 
arranged  that  either  the  whole  or 
only  one-half  of  the  machine 
may  be  used  at  one  tune.  In  its 
later  form  it  is  driven  from*  the 
centre  of  the  shaft,  and  by 
withdrawing  the  coupling  bolts 
one-half  of  the  shaft  only  is  re- 
volved. The  scrubbing  appliance 
differs  from  that  in  other 
machines  in  that  it  consists  of  a 
number  of  brushes  made  from 
foreign  bass  and  attached  to  a 
framework  carried  from  the  cen- 
tral shaft.  The  gas  in  passing 
from  bay  to  bay  finds  a  path 
between  the  bristles  of  the  brushes 
and  is,  accordingly,  subjected  to 
most  intimate  contact  with  the 
liquor. 

Clapham's  "Eclipse" 
washer-scrubber  was  one  of  the 
first  to  be  introduced  and  is  still 
in  common  use,  although  some 
modification  has  taken  place  as 
compared  with  the  original 
machines.  It  is  particularly  of 
interest  in  view  of  the  unique 
means  employed  for  bringing  the 
crude  gas  in  contact  with  wetted 
surfaces.  The  outer  case  is  not 
cylindrical,  the  lower  portion 
being  rectangular  and  the  upper 
half  semi-circular.  The  shell,  as 
in  other  machines,  is  divided 
into  a  number  of  compartments 
in  which  cylindrical  cases  (made 
from  cast  iron)  and  having  per- 
forated back  and  front  plates, 
revolve.  These  cases,  which 
vary  in  number  from  8  to  12, 
are  filled  with  wooden  balls.  The 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     343 

balls  are  kept  in  position  in  the  cases  by  means  of  sheet-iron  cover  plates 
arranged  round  the  periphery.  The  balls  vary  from  1£  inches  to  2  inches  in 
diameter,  according  to  the  size  of  the  machine.  They  are  made  from  hard 
sycamore,  and  each  has  a  hole,  half-an-inch  in  diameter,  bored  through  the 
centre.  The  machine  is  so  arranged  that  the  gas  is  caused  to  travel  in  contact 
with  the  balls,  and  thus  becomes  thoroughly  subjected  to  the  action  of  the  liquor. 
In  some  cases  a  series  of  perforated  buckets  have  been  fixed  upon  the  cases, 
and  so  arranged  that  they  pick  up  the  liquor  and  discharge  it  over  the  balls  when, 
at  the  top  of  their  circular  course. 


FIG.  234. — HOLMES'  WASHER-SCRUBBER. 


CENTRIFUGAL  WASHER-SCRUBBERS 

Centrifugal  washer- scrubbers  are  of  comparatively  recent  introduction,  and: 
differ  considerably  from  the  machines  previously  described.  First,  they  are  essen- 
tially of  the  vertical  type,  having  a  series  of  vertical  compartments  through  which 
the  gas  passes  in  sequence.  The  best  known  in  this  country  is  that  made  by  Kirk- 
ham,  Hulett  and  Chandler,  illustrated  in  Fig.  236.  It  consists  of  a  cylindrical) 
cast-iron  vessel  divided  into  a  number  of  chambers  through  which  passes  a  vertical 
shaft.  To  this  shaft  are  attached  specially  shaped  trays,  which,  revolving  at  a 
speed  of  about  100  to  150  revolutions  per  minute,  lift  up  and  spray  the  washing: 
liquid  so  as  to  bring  it  into  intimate  contact  with  the  ascending  stream  of  gas.  The 
number  of  chambers  varies  from  two  to  ten,  according  to  the  purpose  for  which 
the  apparatus  is  required  ;  but,  in  general,  the  machines  composed  of  a  small:  num- 


344 


MODERN  GASWORKS  PRACTICE 


her  of  chambers  are  employed 
for    naphthalene    washing, 
spraying  an  oil  instead  of  gas 
liquor.      The   construction   of 
the   trays    is   best  seen   from 
Fig.  237.     Each  tray  is  com- 
posed   of    a    perforated    rim, 
whilst    depending     from    the 
bottom   are   four  bent  tubes, 
the   sides   of   which   are   also 
perforated.     As  the  shaft   re- 
volves the  liquid  is  forced  up 
the  bent  tubes  into  the  trays, 
whence  it  is   flung  by   centri- 
fugal    force    across    the    gas 
space,  rebounding  again  from 
the  outer   walls  of   the  cylin- 
der,   and    once   more   coining 
in  contact  with  the  gas.     The 
gas  is  admitted  into  the  lowest 
washing     chamber,     passes 
through    the     spray     to    the 
central  opening  in  the  bottom 
of    the     second     chamber, 
thence     through     the    second 
spray,    and    so    on    into   the 
third  and    subsequent    cham- 
bers.     The    washing   medium 
is  admitted  at  the  top  of  the 
vessel,     flows     through     the 
centre  openings  from  chamber 
to  chamber,  and  is  finally  run 
off    at    the    bottom.      In    an 
eisht-chamber  machine    clean 

O 

watqr  admitted  at  the  top  will 
be  discharged  as  16  oz.  liquor, 
and — if  so  desired — the  last 
traces  of  ammonia  may  be 
removed.  This  washer  is 
equally  suitable  for  the  ex- 
traction of  cyanogen  from  the 
gas.  When  used  for  this  pur- 
pose the  sprayers  are  made 


entirely  of  cast  iron.    For  naphthalene  removal  the  machine  is  constructed  of  from 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     345 


FlG.    236. — KlRKHAM,    HULETT   AND    CHANDLER'S   CENTRIFUGAL   WASHER-SCRUBBER. 

2  to  6  chambers,  but  one  machine  may  be  used  for  both  purposes,  arrangements 
being  made  so  that  one  or  two  chambers  are  supplied  with  water  gas  tar  or  other 
solvent  whilst  the  remainder  are  operated  with  liquor.  The  upper  chambers 


346 


MODERN   GASWORKS   PRACTICE 


should  preferably    be  used   for   naphthalene   removal,    and   the    lower   ones   for 
ammonia  extraction. 

The  Dempster-Feld  washer  (Fig.  238)  is  similar  to  that  described  above  in  so  far 
as  it  consists  of  a  number  of  superimposed  chambers,  through  which  passes  a  vertical 
shaft  rotating  at  a  speed  of  about  120  revolutions  per  minute.  The  spraying  device,, 
which  is  similar  in  all  chambers,  and  is  shown  in  detail  in  Fig.  239,  is  composed  of  a 
number  of  cones,  varying  from  six  to  twelve,  attached  to  the  shaft  by  means  of  a 
cast-iron  hub.  The  lower  ends  of  the  cones  are  so  arranged  that  they  dip  into  the 
liquor  contained  in  the  dish-shaped  channel  in  the  base  of  the  chambers.  As  the  shaft 
rotates,  the  water  is  drawn  up  through  the  spaces  between  the  cones,  and  is  thrown 
off  at  a  tangent  at  the  upper  edge  with  tremendous  velocity,  and  passes  across  the 
gas  space.  The  base  of  each  compartment  is  provided  with  four  apertures  through 
which  the  gas  travels  from  chamber  to  chamber,  entering  at  the  base  and  leaving 


FIG.  237. — CENTRIFUGAL  WASHER-SCRUBBER.    DETAIL  OF  SPRAYING  DEVICE. 


at  the  apex.  A  machine  dealing  with  3  million  cubic  feet  per  day  is  only  5  feet  in 
diameter  and  23  feet  high  over  all,  which  includes  the  height  of  the  pier  on  which 
the  machine  stands.  A  baffle  plate  is  fixed  in  the  outlet  compartment  of  the  washer, 
which  ensures  the  gas  passing  away  in  a  dry  state.  The  washers  are  made  in  sizes, 
varying  from  250,000  to  45,000,000  cubic  feet  of  gas  per  24  hours. 


HOESE  POWER  REQUIRED  BY  WASHER-SCRUBBERS 

The  power  required  to  drive  washer-scrubbers  depends  upon  the  size  of  scrub- 
bers, the  speed  of  running,  and  the  washing  medium  employed,  i.e.  weak  or  strong 
liquor,  tar  or  oil.  Speed  for  speed  the  horizontal  types  absorb  the  larger  amount 
of  power,  but  owing  to  the  very  much  greater  rate  at  which  the  vertical  machines 
travel  they  are  usually  rather  more  extravagant  in  this  direction.  The  following 
figures  (relating  to  the  Kirkham,  Hulett  and  Chandler  washers)  show  the  approxi- 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     347 


mate  powers  required  for  various 
sizes  of  machines ;  t>ut  when  install- 
ing driving  plant  for  this  purpose  it 
is  advisable  to  allow  some  further 
margin  (say  20  per  cent.)  for  contin- 
gencies : — 


Cubic  feet. 
500,000  per  diem 

1,000,000  „ 
2,000,000  „ 
3,000,000 


Horizontal, 
.     3  h.p.      . 

,     4  h.p.     . 

5  h.p.     . 

.     6  h.p.     . 


Vertical. 

4  h.p. 

5  h.p. 
7h.p. 
10  h.p. 


FIG.  239. — DEMPSTER-FELD  WASHER 
SPRAYING  CONES. 


From  this  it  will  be  seen  that  if  elec- 
trical energy  is  used  the  cost  per  day 
for  driving  a  3  million  cubic  feet  ver- 
tical machine  would  amount  to  8s.,  or 
about  -033<Z.  per  1,000  cubic  feet  of 
gas  treated,  or  0-4cZ.  per  ton  of  coal, 
with  electricity  at  a  halfpenny  per 
unit. 


FIG.  238. — THE  DEMPSTER-FELD  CENTRIFUGAL 
WASHER. 


.348 


MODERN   GASWORKS   PRACTICE 


SCRUBBERS 

Scrubbers  of  some  form  or  other  are  almost  universally  employed  for  removing 
the  last  traces  of  ammonia  from  coal  gas.  They  consist  of  either  rectangular  or 
cylindrical  vessels,  the  height  of  which  is  comparatively  great  in  relation  to  the 
width  or  diameter.  The  ratio  of  height  to  diameter  usually  varies  between  2£ 
and  5  to  1,  although  in  some  instances  it  may  be  as  much  as  7  to  1,  particularly  in 
the  case  of  scrubbers  of  comparatively  small  capacity.  The  cylindrical  section 
is  nearly  always  adopted,  and  the  majority  of  scrubbers  are  constructed  from  cast- 
iron  plates  bolted  together  so  as  to  form  tiers.  At  the  bottom  of  each  tier  or  bay 
a  grid  is  fixed  to  brackets  cast  on  to  the  side  plates  whilst  the  gas  outlet  pipe,  in 
many  forms,  passes  down  the  centre  of  the  vessel.  Steel  has  been  employed  to 
some  extent  in  the  construction  of  scrubbers,  the  ring  sections  being  riveted  up 
by  lap  or  butt  joints,  with  external  angles  at  the  top  and  bottom  of  the  sheet.  Owing 
to  its  superior  endurance  against  corrosion  cast  iron  is,  however,  still  preferred 


I 

i 


i 


240. — TYPICAL  JOINTS  IN  CAST-IRON  WORK. 


by  many  engineers.  Cast  iron  possesses,  moreover,  a  secondary  advantage  in 
that  the  vessel  is  easily  taken  to  pieces,  and  may  be  sold  and  re-erected  elsewhere 
when  it  may  have  been  outgrown  by  the  increased  output  of  the  works. 

In  cast-iron  work,  as  in  common  use  for  the  construction  of  scrubbers,  washers, 
tanks,  purifiers,  etc.,  three  types  of  joint  are  found.  These  are  shown  in  Fig.  240. 
It  must  be  emphasized  that  although  rust  joints,  composed  of  iron  borings  and 
cement  (see  page  159)  are  extremely  strong  they  are  not  altogether  desirable  when 
.such  substances  as  ammoniacal  liquor  are  being  dealt  with,  so  that  faced  joints 
should  preferably  be  employed.  For  smaller  scrubbers  (say  up  to  5  feet  diameter) 
the  depth  of  the  cast-iron  plates  is  4  feet,  whilst  above  this  size  5  feet  plates  are 
used.  When  the  diameter  of  the  scrubber  is  exceptionally  large  (over  30  feet) 
the  flat  cast-iron  top  becomes  decidedly  cumbersome,  and  is  liable  to  sag.  In 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS      349- 

such  cases  it  may  be  advisable  to  construct  a  domed  top  having  a  rise  equal  to  one- 
sixth  of  its  diameter  and  made  from  steel. 

The  function  of  the  scrubber  is  to  bring  the  partly  purified  gas  in  contact  with 
large  areas  of  wetted  surface,  and  to  this  end  the  tower  is  packed  with  various 
materials  which  are  laid  on  the  grids  at  the  base  of  each  tier  of  plates.  The  type 
of  packing  required  and  its  disposition  have  no  little  influence  on  the  efficiency  of 
the  scrubber,  hence  considerable  care  should  be  given  to  this  point.  The  chief 
points  to  be  kept  in  mind  when  deciding  upon  the  method  of  packing  are  the 
following  : — 

(1)  A  large  area  of  exposed  surfaces  is  required. 

(2)  The  surfaces  should  be  rough. 

(3)  Any  tendency  for  the  gas  to  "  slip  "  must  be  avoided,  and  the  stream  should 
be  broken  up  as  far  as  possible. 

(4)  Initial  cost  of  the  packing  material. 

(5)  The  life  of  the  material. 

(6)  Ease  of  cleaning  out. 

Brushwood  and  fascines  were  largely  used  as  a  packing  in  by-gone  days,  but 
have  now  been  superseded  by  layers  of  coke,  wooden  blocks,  drain-pipes,  grids,, 
and  boards  on  edge.  As  regards  the  relative  areas  exposed  to  the  gas  by  these 
materials,  Livesey  has  given  the  following  figures  : — 

Coke          ,-•        .         f'       .       8J  square  feet  per  cubic  foot  of  scrubber  capacity. 
Drain-pipes,  3  inch  diameter  17  ,,  „  „          „  „ 

2  inch         „         21  „ 

Boards  on  edge  .     31  „  „  „          „  „ 

Dr.  Carpenter  has  obtained  extremely  high  efficiency  by  packing  scrubbers 
with  metal  bundles  somewhat  similar  to  those  employed  in  Kirkham,  Hulett  and 
Chandler's  horizontal  washer-scrubber  (Fig.  231).  There  is  little  doubt,  however, 
that,  considering  efficiency  in  conjunction  with  expense,  it  is  difficult  to  improve 
on  a  packing  composed  of  boards*  placed  on  edge.  These  should  be  rough  sawn 
and  arranged  in  chequer  fashion,  so  as  to  give  a  sieve-like  construction.  The  size 
of  boards  conforms  to  no  hard  and  fast  rule.  The  following  may,  however,  be  taken 
as  affording  satisfactory  results  : — 

6-inch  boards,  j  inch  thick,  laid  f  inch  apart. 

11-inch  boards,  |  inch  thick,  laid  |  inch  to  f  inch  apart. 

A  typical  tower  scrubber  complete  with  board  filling  is  shown  in  Fig.  241.  In 
this  case  the  bottom  compartment  forms  a  washer  for  the  purpose  of  tar  removal.. 

Board  or  grid  filling  for  scrubbers  is  somewhat  costly  in  the  first  instance,  and 
where  expense  is  of  material  importance  tiers  of  coke  may  be  substituted.  Approxi- 
mately, board  filling  will  cost  four  times  more  than  coke  tiers,  but  it  may  be  made 
use  of  over  and  over  again.  Whatever  type  of  filling  is  employed  it  is  essential 
that  the  upper  surface  of  each  layer  should  not  be  in  contact  with  the  underside  of 
the  grid  supporting  the  layer  above  it,  otherwise  irregular  distribution  of  gas  and 
liquor,  also  increased  back-pressure,  will  result.  When  the  distance  between  the; 


350 


MODERN   GASWORKS   PRACTICE 


FIG.  241. — TYPICAL  TOWER  SCRUBBER  WITH  WASHER 
AT  BASE. 


tiers  is  5  feet,  at  least  1  foot  of 
clearance  should  be  allowed,  and 
when  4  feet,  6  to  9  inches  is 
advisable. 

Except  in  small  works  it  is 
common  to  find  scrubbers  erected 
in  pairs,  whilst  in  the  largest 
works  there  may  be  batteries  of 
several.  Whatever  the  number, 
it  should  always  be  arranged  for 
the  gas  to  come  in  contact  with 
clean  water  before  going  forward 
to  the  purifiers.  When  two  or 
more  scrubbers  are  in  use  the 
last  should  be  supplied  with  clean 
water  alone,  this  running  out  at 
the  base  as  a  weak  liquor,  which 
is  then  pumped  up  to  the  pre- 
ceding scrubber,  and  so  on. 
When  only  one  scrubber  is  avail- 
able it  should  be  so  operated 
that  the  upper  portion  is  supplied 
with  clean  water,  whilst  the 
lower  tiers  are  treated  with 
liquor  from  an  intermediate 
spray. 

An  effective  scheme  has 
been  introduced  by  Thos.  Glover, 
and  is  illustrated  in  Fig.  242. 
The  scrubbers  are  both  fitted  with 
boards  and  are  supplied  with 
liquor  which  is  previously  passed 
through  a  strainer.  The  second 
scrubber  is  supplied  with  plate- 
glass  windows  placed  opposite 
each  other,  so  that  if  the  vessel  is 
carrying  out  its  work  effectively 
it  is  possible  to  see  clearly  through 
it  from  side  to  side.  Half-way 
from  the  top  weak  liquor  is  sprayed 
on  to  the  boards,  whilst  the  upper 
half  is  supplied  with  clean  water 
alone.  The  liquor  flowing  from 
the  scrubbers  passes  through  a 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     351 


DETAIL  OF 

tf 

j 

o 

ft, 

-—  T^= 

FIG.  242.  —  GLOVER'S  SCRUBBER  ARRANGEMENT. 

//////// 

a 

li 

/ 

r 

i 

S  a 

c«   § 
** 

|'-E 

G  "3 
£* 

sealed  sight  overflow, 
loss  is  prevented. 


In  this  way  the  rate  of  flow  is  readily  seen  and  ammonia 


352 


MODERN   GASWORKS   PRACTICE 

LIQUOR  DISTRIBUTORS 


There  are  many  types  of  liquor  distributors  or  sprays  now  in  use,  the  main  ob- 
ject  being  that  of  ensuring  a  regular  flow.  It  is  also  essential  that  the  scrubbing 
liquid  should  be  spread  over  the  entire  cross -section  in  uniform  quantities, 


FIG.  243. — INVERTED  CONE 
DISTRIBUTOR. 


FIG.  244. — GURNEY'S  JET. 


FIG.  245.- 


-BARKER'S  MILL  OPERATED 
BY  TUMBLER. 


and  atomized  if  possible.  Liquor  distributors  may  be  classified  into  two  sections, 
namely,  those  operated  under  pressure  and  those  in  which  practically  no  head  of 
water  is  available.  Modern  scrubbers  should  preferably  be  fitted  with  a  main 
pressure  box  situated  in  the  centre  of  the  top  cover  plate  of  the  vessel  and  from 
which  arms  radiate  in  various  directions.  The  pressure  of  the  liquor  or  water  is 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     353 


then  maintained  by  a  suit- 
able pump,  and  atomizers 
are  spaced  at  intervals 
through  the  cover  plate. 
For  small  works  where  no 
great  pressure  is  available 
the  ;  best  results  will  be 
given  by  some  simple  means 
such  as  the  inverted  cone 
(Fig.  243)  or  Gurney's  jet 
(Fig.  244).  The  well-known 
principle  of  the  Barker's 
mill  is  also  very  effective, 
but  unless  a  certain  amount 
of  head  is  available  the  arms 
of  the  mill  will  remain 
stationary,  with  the  result 
that  local  spraying  will 
occur.  On  this  account  it 
is  the  general  practice  to 
employ  the  device  known  as 
the  "  tumbler,"  particularly 
when  the  amount  of  water 
entering  the  scrubber  is  so 
small  as  to  be  little  more 
than  a  trickle.  The  sudden 
discharge  of  the  tumbler, 
taking  place  at  intervals, 
creates  a  certain  amount  of 
velocity  head,  which  causes 
the  arms  of  the  mill  to 
rotate  for  a  short  period. 
A  complete  installation  of 
a  tumbler  and  Barker's  mill 
is  shown  in  Fig.  245.  Fig. 

246  shows  another  means  of 
operating   the   mill   without 
the    tumbler,     and,     conse- 
quently, is  applicable  where 
a  moderately  full  stream  of 
liquor    is     available.       Fig. 

247  shows  an  arrangement 

by  means  of  which  the  sprayer  arms,  with  the  aid  of  suitable  gearing,  are  revolved 
by  a  water  wheel.      Some  engineers  prefer  to  arrange  for  an  intermittent  flush 


FIG.  246. 


354 


MODERN  GASWORKS   PRACTICE 


FIG.  247. — WATER  WHEEL  SPRAY. 


FIG.  248.— MANN'S  Discs. 

of  liquor  rather  than  a  continuous  flow,  and  in 
such  cases  the  tumbler  may  be  conveniently 
employed.  Another  means  of  providing  for 
intermittent  flow  is  by  introducing  the  principle 
of  Mann's  discs  (Fig.  248).  The  upper  disc 
revolves  whilst  the  lower  remains  stationary, 
so  that  when  the  holes  in  the  discs  coincide  a  flush  of  water  or  liquor  is  given. 

THE   CAPACITY   OF  WASHERS   AND   SCRUBBERS 

The  necessary  capacity  of  the  washing  and  scrubbing  plant  depends  very  largely 
on  the  type  of  apparatus  employed.  Owing  to  the  introduction  of  more  efficient 
plant  the  size  of  the  vessels  has  undergone  some  considerable  reduction  of  late 
years.  For  washers  of  the  Livesey  and  similar  types  the  following  rule  is  reliable  : — 

Allow  \  to  1  cubic  foot  of  capacity  per  1,000  cubic  feet  of  gas  passed  per  diem. 

The  standard  sizes  of  Livesey  washers  for  dealing  with  various  quantities  of 
gas  may  be  taken  as  follows : — 


Gas  dealt  with  per  2"4  Hours. 

Length  and  Width 
of  Washer. 

Depth 
of  Washer. 

ft.    in.  ft.  in. 

ft.    in. 

3i-4  million  cubic  feet        .... 

20    0X7     6 

3     6 

21-3       „             „„.... 

15     0X7     6 

3     6 

U-2       „             „        „         .... 

10     0X7     6 

3     6 

H     »         „„.... 

5    0X7     6 

3     6 

500-750,000        „         

6    0X4    0 

3    0 

300-500,000       „         

5     0x3     6 

2    6 

200-250,000       „        

3     0x4    0 

2    6 

75-100,000         „                  .... 

3    8x1     3 

2     6 

For  mechanical  washer-scrubbers  an  allowance  of 
passed  per  diem  may  be  made. 


to  f  cubic  foot  per  1,000  cubic  feet  of 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     355 

i 

SCRUBBERS 

When  there  is  no  other  wet  purification  plant,  a  generally  recognized  rule  for 
the  capacity  of  tower  scrubbers  states  that  9  cubic  feet  of  volume  should  be 
allowed  for  every  1,000  cubic  feet  of  gas  passed  per  diem.  For  modern  requirements, 
however,  so  great  an  allowance  will  in  most  cases  prove  unnecessary ;  but  much 
depends  upon  the  washing  apparatus  prior  to  the  scrubbing  plant.  In  the  scrub- 
bers slow  contact  is  desirable,  so  that  the  gas  should  be  in  contact  with 
the  wetted  surfaces  for  a  period  of  from  ten  to  fifteen  minutes,  as  against  about 
twenty  seconds  in  the  modern  form  of  washer- scrubber.  When  associated  with 
any  form  of  mechanical  washing  apparatus  5  or  6  cubic  feet  of  scrubber  capacity 
per  1,000  cubic  feet  of  gas  per  diem  should  prove  ample.  In  some  cases  the  gas 
issuing  from  the  power-driven  vessel  is  practically  devoid  of  ammonia,  and  is  merely 
passed  through  a  small  tower  scrubber  operated  with  clean  water  and  working  as 
a  catch  vessel.  Such  a  scheme,  however,  is  not  to  be  recommended,  unless  ample 
safeguards  are  provided  against  the  breakdown  of  the  mechanical  machine.  Where 
no  washer-scrubbers  are  in  use  the  capacity  allowed  should  be  as  much  as  10  cubic 
feet  per  1,000  cubic  fest  of  gas  per  diem.  This  includes  both  washer  and  scrubber 
capacity  in  such  cases  where  only  board-filled  washers  and  coke  or  board  scrub- 
bars  are  employed,  and  may  be  apportioned  half  to  the  one  type  of  vessel  and  half 
to  the  scrubbers.  When  washers  on  the  Livesey  and  such  principles  are  introduced 
the  scrubber  allowance  need  be  no  more  than  6  cubic  feet  per  1,000  cubic  feet  of 
gas  per  diem.  In  very  small  works  where  one  tower  scrubber  alone,  and  no  washer, 
is  in  operation,  the  allowance  may  wisely  be  increased  to  12  cubic  feet. 

The  following  are  the  sizes  of  scrubbers  which  may  be  effectively  employed 
for  the  removal  of  ammonia  where  no  other  plant  (i.e.  washers)  is  in  use  for  this  pur- 
pose. In  giving  the  actual  size  of  scrubbers  this  is  the  only  case  which 
can  be  readily  dealt  with,  when  no  details  of  the  washing  apparatus  are  known. 


SINGLE  SCRUBBERS 


SCBUBBEB. 

Diameter. 

Height. 

ft.    in. 

ft.    in. 

20,000  cubic  feet       

3     6 

24    0 

40,000       „       „          

4    6 

32    0 

60,000       „       „          

5    0 

36    0 

80,000       „       „          

6    0 

35    0 

100,000       „       „          

7    0 

35    0 

150,000       „                  

8     0 

35     0 

200,000       „       „          

9    0 

40     0 

300,000       „       „          

10    0 

40     0 

356  MODERN   GASWORKS   PRACTICE 

Two  SCRUBBERS  IN  SERIES 

ft.    in.  ft.    in. 

100,000  cubic  feet     .  .  ,.  .  50  30  0          each 

200,000                „     "f  .  .  .  60  35  0       scrubber 

300,000      „         „      '.  .  .  70  40  0      of  these 

500,000      „         „  .  .  90  40  0      dimensions. 

1,000,000      „         „       .  .  .  .  12     0  45  0 

1,500,000      „        „      .  -     ,  .  :      .  14    0  50    0 

It  will  be  noticed  that  for  the  smaller  scrubbers  the  ratio  of  diameter  to  height ' 
is  very  much  greater  than  is  the  case  with  the  larger  capacity  vessels.  In  the  case 
of  single  scrubbers  it  will  be  seen  that  works  making  up  to  300,000  cubic  feet 
per  diem  have  only  been  considered,  as  it  is  inconceivable  that  larger  concerns 
than  this  would  be  provided  with  one  scrubber  alone.  The  same  remarks  apply  to 
the  two  scrubbers,  where  the  limit  has  been  placed  at  1^  million  cubic  feet  per 
day.  It  cannot  be  urged  too  strongly  that  the  process  of  condensation  should  be 
carried  out  in  an  adequate  and  scientific  manner.  Effective  condensation  means 
an  enormous  reduction  in  the  requisite  scrubber  capacity. 

AMOUNT  OF  WATER  REQUIRED 

No  hard  and  fast  rule  can  be  laid  down  in  connexion  with  the  amount  of  water 
necessary  to  remove  completely  the  ammonia  from  the  gas.  Much  must  depend 
on  the  amount  of  this  compound  present,  and  on  the  proportion  of  it  which  is  elimin- 
ated and  thrown  down  in  the  virgin  liquor  of  the  condensers,  etc.  It  has  been 
stated  that,  theoretically,  the  whole  of  the  ammonia  may  be  removed  by  admit- 
ting 3  gallons  of  water  per  ton  of  coal  carbonized,  but  in  practice  such  a  result 
is  never  attained.  In  the  ordinary  way,  the  whole  of  the  water  employed  is  ad- 
mitted to  the  final  or  clear- water  scrubber,  and  in  normal  cases  this  amounts  to 
10  to  13  gallons  per  ton  of  coal  carbonized.  Much,  however,  depends  upon  the 
type  of  scrubber  in  use,  coke  filling  requiring  a  greater  quantity  of  water  than  is 
the  case  with  board  filling.  Much  variation  is  shown  in  the  direction  of  water  con- 
sumption, and  the  author  can  point  to  cases  where,  with  no  other  washing  appara- 
tus but  scrubbers  in  use,  the  quantity  admitted  amounts  to  only  4  gallons  per 
ton  of  coal.  The  horizontal  washer- scrubber  does  not  effect  any  marked  economy 
in  water,  and  in  most  cases  requires  an  amount  equal  to  about  10  gallons  per  ton 
of  coal.  Vertical  washer-scrubbers  of  the  centrifugal  type  are,  however,  very  much 
more  efficient  in  this  respect,  and  a  small  quantity  of  water,  admitted  at  the  top, 
will,  if  desired,  remove  the  whole  of  the  ammonia.  At  Salisbury  it  was  found  that 
with  clean  water  admitted  to  a  vertical  machine  at  the  rate  of  3f  gallons  per  ton 
of  coal  carbonized  90  per  cent,  of  the  ammonia  present  in  the  gas  at  the  inlet  was 
retained,  whilst  the  water  passed  off  as  a  16  oz.  liquor.  Thos.  Glover  has  given 
fi  gures  for  the  quantity  of  liquor  which  should  be  distributed  in  scrubbers  in  order 
that  these  vessels  may  perform  their  work  most  efficiently.  He  states  that  the 
liquor  distributed  per  square  foot  of  cross-sectional  area  of  the  scrubber  should 
be  0-145  gallons  per  minute.  This  is  less  the  clean  water  added  to  the  final 
scrubber. 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     357 

AMMONIA   LOST   THROUGH   SCRUBBERS 

Many  engineers,  nowadays,  make  a  practice  of  allowing  a  very  small  amount 
of  ammonia  to  travel  forward  from  the  scrubbers  to  the  purifiers.  In  this  way 
the  oxide  of  iron  is  maintained  in  an  alkaline  condition  and  fulfils  its  functions 
more  satisfactorily.  The  amount  of  ammonia  permitted  to  travel  forward  varies 
from  0-5  to  1  grain  per  100  cubic  feet. 

In  making  tests  for  the  quantity  of  ammonia  passing  through  the  scrubber 
it  is  preferable  to  calculate  the  total  ammonia  loss  rather  than  to  state  the  quantity 
in  so  many  grains  per  100  cubic  feet  of  gas.  Only  by  considering  the  total  quan- 
tity of  gas  passed  can  the  actual  loss,  which  should  be  stated  in  the  equivalent  of 
so  many  gallons  of  8  oz.  or  10  oz.  liquor,  be  gauged.  The  following  is  the  method 
of  making  the  calculation : — 

Total  grains  of  ammonia  lost  per  week 

Gas  made  for  week       No.  of  grains  per  100  cubic  feet  at  scrubber 

- — _      V*  A 

100  outlet. 

In  1  gallon  of  10  oz.  liquor  there  are  1,522  grains  of  ammonia. 
. ' .  Quantity  of  10  oz.  liquor  lost  (in  gallons) 

Total  grains  of  ammonia  lost  per  week 
1,522 


LIQUOR  PURIFICATION 

Attempts  have  been  made  to  dispense  with  dry  purification  plant  by  mak- 
ing use  of  the  alkaline  impurity  (ammonia)  for  removing  the  whole  of  the  remain- 
ing acid  substances.  As  previously  pointed  out,  however,  the  available  ammonia 
in  coal  gas  (after  the  condensers  have  been  passed),  amounts,  theoretically,  to  only 
half  the  quantity  necessary  for  extracting  the  acid  impurities.  It  has  been  pro- 
posed to  overcome  the  difficulty  of  this  deficiency  by  causing  the  ammonia  to  per- 
form its  duties  twice ;  in  other  words,  having  absorbed  the  acid  impurities  the 
resultant  salts  are  decomposed  in  special  apparatus,  when  the  acid  gases  are  expelled 
and  the  ammonia  rendered  available  for  further  use.  Purification  systems  based 
on  such  principles  were  introduced  by  Claus,  also  Laming,  Livesey,  and  Hills. 
Although  theoretically  ingenious,  their  complicated  nature  prevented  any  develop- 
ment on  a  practical  scale. 

THE  GLAUS  PROCESS 

The  Claus  process  is  of  particular  interest,  in  that  it  was  tried  on  a  fairly  large 
practical  scale  at  the  Belfast  gasworks,  but  was  ultimately  abandoned  as  unsuit- 
able. Simply  explained,  the  process  consists  of  the  following  : — 

1.  The  crude  liquor  (i.e.  saturated  with  sulphuretted  hydrogen  and  carbon 
dioxide)  from  the  washers  is  passed  through  a  series  of  towers,  where  it  is  submitted 


358  MODERN   GASWORKS   PRACTICE 

to  the  action  of  carbon  dioxide  gas.     Sulphide  of  ammonia  is,  therefore,  converted 
into  the  carbonate  whilst  sulphuretted  hydrogen  is  liberated. 

2.  The  sulphuretted  hydrogen  gas  is  then  burned  in  a  Glaus  kiln  and  yields  solid 
sulphur. 

3.  The  crude  liquor,  now  consisting  chiefly  of  ammonium  carbonate,  is  passed 
into  heating  towers,  in  which  its  temperature  is  raised  to  frcm  18C°  to  £CO°Fahr. 
In  this  way  the  CO  2  is  expelled  from  the  liquor  to  the  extent  of  from  60  to  75  per 
cent,  of  the  quantity  in  which  it  is  present.     This  C02,  or  rather  a  portion   of  it, 
provides  the  C02  gas  current  mentioned  under  (1).  . 

4.  The  partly  purified  liquor  from  which  the  C02  has  been  liberated  is  then 
distilled  so  that  ammonia  gas  and  the  remaining  ammonium  carbonate  are  evolved . 

5.  The  ammonia  gas  and  ammonium  carbonate  vapour  are  then  passed  through 
cooling  towers,  when  the  carbonate  sublimes  to  the  solid  state,  leaving  a  compar- 
atively pure  ammonia  gas. 

6.  Lastly  the  ammonia  is  admitted  to  the  stream  of  crude  coal  gas  before  the 
latter  enters  the  washers. 

In  this  way  the  original  ammonia  which  has  combined  with  CO  2  andSH2  in 
the  crude  gas  is  recovered  in  the  gaseous  form  and  caused  to  react  once  more  with 
the  acids.  A  surplus  of  ammonia  is,  oi  course,  obtained,  and  may  be  converted 
into  sulphate  of  ammonia  in  the  ordinary  way. 

DAVIDSON'S  PROCESS 

The  most  recent  process  for  the  self- purification  of  crude  gas  is  that  introduced 
by  Dr.  W.  B.  Davidson.  The  principle  of  the  process  is  on  the  same  lines  as  those 
attempted  by  previous  experimenters,  but  it  is  operated  in  a  more  scientific  manner. 
The  process  of  separating  the  acid  gases  from  the  ammonia  is  carried  on  in  a  ver- 
tical still  of  the  usual  pattern,  to  the  top  of  which  the  liquor  is  fed.  The  still  is 
heated  by  steam  introduced  at  the  base,  and  whilst  the  ammonia  is  taken  off  at 
a  point  half-way  up  the  column,  the  C02  and  SH2  are  expelled  at  the  top.  This 
separation  of  the  ammonia  and  acid  gases  is  made  possible  by  graduating  the  tem- 
perature and  pressure  within  the  still — the  pressure  being  so  regulated  that  a  com- 
paratively high  pressure  is  obtained  in  the  portion  of  the  still  from  which  the  am- 
monia is  collected.  After  leaving  the  still,  the  gaseous  ammonia  is  passed  through 
absorbers  to  remove  any  traces  of  the  acid  gases,  and  is  then  re-mixed  with  the  crude 
coal  gas  at  any  convenient  point,  such  as  the  condensers  or  washers.  From 
the  washers,  scrubbers,  and  condensers,  the  ammoniacal  liquor  is  collected  and 
returned  to  the  still,  whilst  the  surplus  ammonia,  being  recovered  in  an  extremely 
pure  form,  provides  a  valuable  by-product.  The  working  pressures  in  the  still 
amount,  as  a  minimum,  to  approximately  5  Ibs.  per  square  inch  at  the  point  where 
the  steam  is  applied ;  4  Ibs.  per  square  inch  where  the  ammonia  is  withdrawn ; 
and  3  Ibs.  per  square  inch  at  the  zone  where  the  acid  gases  are  removed.  Higher 
pressures  than  these  (worked  in  the  same  ratio)  will,  however,  give  more  satisfac- 
tory results.  Though  not  essential  to  the  process,  Dr.  Davidson  prefers  to  treat 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     359 


SH,  and  CO,  Outlet 


Liquor  Inlet 


Ammonia  Outlet 


the  gas  which  has  passed  the  ordinary  washers  and 
scrubbers  with  a  sludge  of  ferrous  hydrate,  prepare'd 
from  iron  chloride  or  sulphate  and  ammoniacal 
liquor.  In  this  way  the  whole  of  the  sulphuretted 
hydrogen  may  be  removed.  The  process  then  re- 
solves itself  into  the  following  :— 

1.  Tar  extractor. — Tar  in  crude  gas  reduced  to 
less  than  2  grains  per  ICO  cubic  feet. 

2.  Cyanogen  washer. — Iron  sulphide  sludge  em- 
ployed for  removing  cyanogen  : — FeS  +  6HCN  + 
4NH3  =  (NH4)4FeC6N6  +  SH2.     Ammonium  ferro- 
cyanide  is  thereby  formed,  with  the  liberation    of 
sulphuretted  hydrogen. 

3.  First    ammonia    washer.  —  To     which   the 
ammonia  gas  liberated  from  the  liquor  is  admitted, 
thus    extracting   the    bulk    of    the    sulphuretted 
hydrogen  and  carbon  dioxide. 

4.  Second  ammonia  washer. — In  which  water  is 
used   for  removing  any  remaining  ammonia,  SH2 
and  C02.     The  SH2   is   reduced  to   less  than  0-C2 
per  cent,  by  volume. 

5.  Final  ivaslier. — In  the  lower  portion  of  this 
washer,  a  ferrous  hydrate  sludge  is  used  to  extract 
the  last  traces  of   SH2  and  a   further  quantity  of 
ammonia,  as  follows  : — 

Iron    sulphate    is    treated    with    ammoniacal 
liquor   to    give   ammonium   sulphate.       FeS04  -f- 

2NH4OH  =  (NH4)2S04  +  Fe(OH)2.  The  SH2  then  combines  with  the  iron  hydrate 
formed  :— Fe(OH)2  +  SH2  =  FeS  +  2H20.  The  iron  sulphide  resulting  from  this 
reaction  is  afterwards  made  use  of  for  absorbing  cyanogen,  as'  explained  under 
heading  (2).  In  the  upper  portion  of  the  final  washer,  water  or  sulphuric  acid  is 
used  for  extracting  the  last  traces  of  ammonia. 


Steam  Inlet 


Waste  Liquor  Outlet 

FIG.  249. — DAVIDSON'S  AMMONIA 
STILL. 


DIRECT  METHODS  OF  RECOVERY 

During  refcent  years,  some  considerable  attention  has  been  given  to  the  pro- 
blem of  recovering  the  ammonia  resulting  from  the  distillation  of  coal  by  direct 
means.  In  the  ordinary  way,  this  ammonia  is  wholly  recovered  in  the  foim  of 
an  ammoniacal  liquor,  the  liquor  being  subsequently  worked  up  into  sulphate  of 
ammonia  in  a  distinct  plant.  Chemists,  particularly  on  the  Continent,  have  en- 
deavoured to  obviate  the  necessity  for  providing  a  separate  unit  for  working  up 
the  ammonia  into  commercial  form,  and  have  introduced  processes  for  the  "  direct  " 
recovery  of  the  by-product  in  the  ordinary  course  of  gas-making.  The  "  direct  '* 


360 

methods  now  employed  for  the  recovery  of  ammonia  may  be  classified  under  two 
headings,  namely : — 

(a)  Those  in  which  the  acid  impurity,  sulphuretted  hydrogen,  is  utilized  to  form 
sulphate  of  ammonia. 

(6)  Those  in  which  the  crude  gas  is  passed  through  a  seal  of  sulphuric  acid, 
thereby  causing  sulphate  of  ammonia  to  be  deposited.  These  processes  are  some- 
times referred  to  as  "  semi-direct "  methods. 

The  ideal  process  is  undoubtedly  that  in  which  the  use  of  sulphuric  acid  is  un- 
necessary. Although  the  practical  difficulties  attending  such  methods  are  many, 
Burkheiser  and  Feld  have  already  met  with  some  considerable  success  in  this  direc- 
tion, and  their  schemes  may  now  be  said  to  be  beyond  the  experimental  stage. 
They  cannot,  however,  lay  claim  to  having  reached,  as  yet,  a  stage  of  perfection. 

THE  BURKHEISER  PROCESS 

In  Burkheiser's  process,  the  usual  practice  of  extracting  ammonia  prior  to  sul- 
phuretted hydrogen  is  reversed — the  sulphur  impurities  being  removed  first.  The 
modus  operandi  of  the  plant  can  be  followed  best  by  referring  to  the  diagram, 
Fig.  250.  The  crude  gas  coming  away  from  the  tar  extractor  is  first  pre-heated 
by  means  of  a  steam  coil.  It  then  travels  through  a  form  of  still,  where  the  am- 
monia is  expelled  from  any  virgin  liquor  thrown  down  in  the  condensers,  etc.,  and 
is  carried  forward  by  the  crude  gas.  The  sulphuretted  hydrogen  is  then  extracted 
by  passing  the  gas  through  purifiers  containing  Burkheiser's  patent  oxide.  This 
oxide  has  been  subjected  to  a  special  process  of  roasting,  by  means  of  which  the 
organic  matter  and  moisture  are  removed,  leaving  the  material  in  the  form  of  small 
nodules.  The  activity  of  the  oxide  is  so  increased  by  this  means  that  it  is  capable 
of  removing  sulphuretted  hydrogen  at  a  speed  thirty  times  greater  than  is  the  case 
with  ordinary  oxide.  The  apparatus  is  in  two  similar  sections,  one  portion  being 
used  for  purifying  the  gas  whilst  the  other  is  given  up  to  revivification  of  the  oxide. 
The  two  sections  change  places  at  intervals — the  one  which  was  revivifying  doing 
the  purification,  and  vice  versa.  After  leaving  the  ammonia  still,  the  gas  passes 
through  special  oxide  of  iron  in  the  purifier  and  thence  into  the  base  of  the  am- 
monia washer.  An  acid  solution  is  admitted  to  the  top  of  the  washer,  and  in  this 
way  the  ammonia  is  neutralized  and  washed  out  from  the  gas.  The  neutral  liquor, 
or  lye,  flowing  from  the  washer  is  collected  and  used  in  the  other  side  of  the  plant. 
The  gas,  free  from  all  impurities,  passes  out  at  the  top  of  the  ammonia  washer  as 
shown. 

When  the  oxide  has  absorbed  its  maximum  quantity  of  SH2,  the  gas  is  deflected 
from  the  right-hand  side,  and  is  passed  through  the  left-hand  side  of  the  plant, 
where  the  oxide  (previously  fouled)  has  been  undergoing  revivification ;  whilst 
the  former  purifying  side  is  now  submitted  to  an  air-blast,  so  that  this  oxide  may 
be  revivified.  Kevivification  is  carried  out  by  passing  a  powerful  air-blast  through 
the  spent  oxide,  and  the  compounds  of  sulphur  and  iron  are  violently  oxidized  so 
that  sulphurous  acid  is  produced.  The  air-blast  (laden  with  the  acid)  then  passes 


THE   PRELIMINARY   PURIFICATION   OF   COAL   GAS     361 

to  the  washer,  where  it  meets  with  a  stream  of  neutral  liquor  produced  in  the  other 
side  of  the  plant — this  absorbing  the  acid  gases  and  running  out  as  an  acid  lye  from 
the  bottom  of  the  washer.  This  acid  liquor  is  then  pumped  over  to  the  opposite 
side  of  the  plant,  and  is  utilized  for  absorbing  ammonia  as  before  explained.  A 


Neutral  Lye 


Virgin  Liquor 


FIG.  250. — LINE  DIAGRAM  SHOWING  BURKHEISER'S  PROCESS. 


definite  volume  of  liquor  is  thus  kept  in  circulation,  and  becomes  gradually  charged 
with  salt  until  the  saturation  point  is  reached,  when  the  salt  is  deposited  at  the 
bottom  of  the  neutral  lye  tank  as  ammonium  sulphite  and  sulphate,  the  reaction 
being:— H20  +  S02+2NH3=(NH4)2S03  (sulphite).  The  sulphite  is  then  oxidized 
into  sulphate,  taking  up  another  atom  of  oxygen  from  an  air-blast.  For  this  pur- 


362  MODERN   GASWORKS    PRACTICE 

pose  the  apparatus  shown  in  Fig.  251  is  used,  the  sulphite  being  first  heated  by 
a  steam  jacket  and  sublimed  thereby. 

The  cylinder  in  which  the  worm  conveyor  works  is  jacketed  for  the  first  half 
of  its  length  with  cold  water,  and  for  the  second  half  with  steam.  The  sulphite, 
on  reaching  the  heated  portion,  is  volatilized  and  driven  back  again  by  a  blast  of 
air  entering  at  the  outlet  end,  this  air  converting  the  sulphite  into  sulphate,  which 
is  then  deposited.  The  principle  of  the  apparatus  is  dependent  upon  the  fact  that 
ammonium  sulphite  is  sublimed  at  temperatures  below  1CO°  C.,  whereas  the  sul- 
phate is  not.  The  salt  thrown  down  in  the  liquor  tank  consists  of  about  67  per 
cent,  sulphite,  and  the  remainder  sulphate. 

In  a  process  of  this  kind  there  is  some  liability  to  accident  owing  to  over-heating 
during  the  revivification  of  the  oxide.  This,  however,  is  guarded  against  by  arrang- 
ing a  system  of  water-cooling  for  the  oxide,  also  by  ensuring  the  presence  of  water 
vapour  in  the  blast.  In  practice,  there  is  little  fear  of  danger  unless  a  tempera- 
ture of  570°  Fahr.  is  exceeded ;  and 

in  Here  in  the  Burkheiser  plant  the  tempera- 

ture rarely  rises  above  285°  Fahr. 
Moreover,  as  a  safeguard,  an  electric 
alarm  thermometer  is  fitted  to  the 
purifier  undergoing  regeneration. 

In  a  process  of  this  kind  there  is,  of 
course,  an  excess  of  sulphur  over  that 
necessary  to  neutralize  the  whole  of 
the  ammonia.  This  surplus  may  be 

sulphate  out  Here.,  \       /  recovered  for  sale  in  various  ways. 

Air  mast  The  sa^  obtained  by  the  process  is 

FIG.  25i.-BuRKHEisER's  OXIDATION  APPARATUS.      of  a  somewhat  inferior  quality,  owing 

to  the  incomplete  nature  of  the  oxi- 
dizing process,  and,  consequently,  the  presence  of  ammonium  sulphite. 

THE  FELD  PROCESS 

The  Feld  plant  affords  another  means  of  arriving  at  the  same  result  as  is 
obtained  in  the  Burkheiser  system,  i.e.  the  recovery  of  ammonia  as  sulphate  of 
ammonia  by  causing  it  to  combine  with  the  sulphur  impurities.  The  Feld  plant 
extracts  ammonia  and  sulphuretted  hydrogen  simultaneously,  at  the  same  time 
oxidizing  an  amount  of  sulphuretted  hydrogen  equivalent  to  the  ammonia  in  the 
gas.  Sulphate  of  ammonia  is  yielded,  whilst  the  surplus  sulphur  is  obtained  in 
the  solid  form.  Within  the  last  year  or  so,  the  plant  has  undergone  some  modifi- 
cation ;  the  original  process  is,  however,  of  considerable  interest,  and  is  described 
in  outline  below.  For  the  sake  of  simplicity,  the  various  stages  in  the  working 
are  sub-divided  under  different  headings,  so  that  there  should  be  no  difficulty  in 
following  out  the  scheme  with  the  aid  of  the  accompanying  diagram  (Fig.  252). 

Process  1. — Gas  containing  NH3andSH2is  washed  with  a  weak  solution  of 


THE   PRELIMINARY    PURIFICATION    OF    COAL    GAS    363 

ferrous  sulphate.     Sulphate  of  ammonia  is  formed,  and  sulphide  of  iron  precipi- 
tated— 

(a)    FeS04  +  2NH4,OH  =  (NH4)2S04   +Fe(OH)2 
(6)   Fe(OH2)  +  SH2  =  FeS  +  2H80 

Process  2. — The  iron  sulphide  liquor  is  treated  with  SO  2,  which  is  obtained  by 
the  burning  of  sulphur.  Free  sulphur  is  precipitated,  and  soluble  ferrous  thio- 
sulphate,  thionate,  and  sulphate  are  formed — 2FeS  +  3S02  =2FeS203  +  S. 

Process  3. — This  liquor  (FeS203)  is  again  used  for  treating  the  gas — 2FeS203 
+  4NH3  +  2H2S  =  2FeS  +  2(NH4)2,S203.  The  reaction  this  time  is  somewhat 
different.  The  ammonia  and  SH2  in  the  gas  are  again  absorbed,  whilst  iron  sul- 
phide, together  with  some  free  sulphur,  is  precipitated — sulphate,  thiosulphate, 
and  thionate  of  ammonia  being  formed.  The  liquor  is  alternately  treated  with 
crude  gas  and  S02  until  it  contains  from  30  to  45  per  cent,  of  ammonia  salts. 


Liquor  with 
30-45  Per  Cent 
Sulphate  of  Ammonia 

<V 
FeS  and 

Evaporator 
acuum  Boiler) 
^  ^ 

Remainder  of  NH, 
and  SB,  Absorbed 
by  Excess  of  — 
FeSO..  FeSA  etc. 

FeSO.  Saturated  by 
NH,  and  SB,  into 
FrS  and  (NH.),SO. 

s 

—  ; 

a 

•«- 

->- 

/ 

A.f 

^\ 

=j 

r  SO,  and  Air 

'. 

into 
1  S.' 

*** 

1 

H^ 

r" 

—=--, 

t  ' 

^^, 

Centrifugal  Washer 

FeS,03.  etc. 
FeSO,  ai 

SO, 

^ 

£]p 

t 

I 

L 

FeS  in 

a 

B 

—•  —  i 

.-  i 

E 

1 

t 

F 
Or 

B 

1 

\    / 

.  

—  »• 

-v  * 

1)    etc. 
Still^ 

\ 
(r<L 

< 

X, 

M 

-»- 

((  )) 

—  C 

t 

Jl 
i 

— 

3_ 

fllL 

Ciller  Press 
(Sulphur 

Jjk 

Uter  Press  ^v 
in  Sulphide)  j 

(NB.),SO. 
Air  Blast 

=***-: 

ft 

IT 

^y 

ind  Air 

\    \ 

j 

-j 

M 

==T 

\ 

~*~ 

t 

A 



~~^  0 

c 



--    - 

f 

1 

FeSO.  and 
<NB.),SO. 

T                     1 

FeS 
FeSA 

JltO 

etc 

FeSO.. 

FeS.O,.  etc. 

J     1 

Sulpb 

1 

ir  Burne 

-1- 

Centrifugal 
Dryer 


FIG.  252. — LINE  DIAGRAM  SHOWING  PRINCIPLE  OF  FELD'S  ORIGINAL  PROCESS. 

Process  4. — The  liquor  undergoes  oxidation,  by  which  process  the  thiosulphate 
and  thionates  are  transformed  into  sulphate.  To  do  this  the  hot  liquor  is  treated 
with  SO  2,  and  an  excess  of  air.  The  ferrous  sulphide  is  dissolved,  and  the  am- 
monia all  converted  into  sulphate,  whilst  free  sulphur  is  precipitated — 2FeS  + 
2(NH4)2,  S203  +  3S02  +  202  **  2(NH4)2,S04  +  2FeS04  +  58. 

Process  5. — The  free  sulphur  is  separated  from  the  liquor  by  nitration. 

Process  6. — The  liquor  coming  from  the  filter- press,  and  containing  the  sulphate 
of  ammonia,  also  sulphate  of  iron,  is  treated  with  the  crude  gas  (containing  SH2 
and  NH3),  by  the  action  of  which  the  ferrous  sulphate  is  decomposed,  forming  again 
sulphate  of  ammonia  and  iron  sulphide  (see  unde*  Process  1).  The  iron  is  separ- 


346  MODERN   GASWORKS   PRACTICE 

ated  by  filtration,  and  the  liquor  containing  the  sulphate  is  evaporated,  leaving 
the  salt  behind — this  being  dried  in  a  centrifugal  machine. 

The  diagram  shows  the  plant  complete.  The  washing  liquor  is  pumped  to 
the  Feld  centrifugal  washer,  and,  on  leaving,  passes  through  the  "  still,"  being 
collected  in  the  lower  tank.  Here  (also  in  the  still)  the  liquor  meets  with  S02, 
which  brings  about  the  regeneration  of  the  FeS  into  sulphates.  As  soon  as  the 
liquor  contains  30  to  45  per  cent,  of  ammonia  sulphate,  it  is  pumped  to  the  upper 
tank,  while  the  lower  one  is  filled  with  fresh  liquor.  The  salts  are  converted  wholly 
into  sulphates  in  this  upper  tank.  The  sulphur  is  then  separated  out  in  the  filter 
press,  and  the  liquor  coming  away  from  this  is  continuously  pumped  round  and 
round  into  the  lowest  bay  of  the  washer.  The  object  of  this  is  to  completely  pre- 
cipitate the  iron  from  the  sulphate  solution.  The  iron  sulphide  mud  is  then  filtered 
out  in  the  second  press,  and  the  liquor  evaporated  and  dried.1 

In  the  Feld  process,  as  recently  modified,  the  use  of  the  iron  or  zinc  salt  is 
discontinued.  As  a  washing  medium,  a  solution  is  used  containing  ammonia, 
sulphur,  and  sulphurous  acid,  also  ammonium  thiosulphate  and  polythionates. 
In  the  washer  the  ammonia  and  sulphuretted  hydrogen  are  absorbed,  with  the 
conversion  of  the  ammonium  polythionate  into  thiosulphate. 

(NH4)2S406  +  2NH3  +  H2S  =  2(NH4)2S203  +  S. 
(Ammonium  Tetrathionate)  (Ammonium  thiosulphate). 

After  a  time,  the  spent  liquor  running  from  the  washer  is  treated  with  S02  from 
the  kiln  and  regenerated  at  about  100°  Fahr— 2(NH4)2S203  +  3S02  +  S  = 
2(NH4)2S406.  This  regenerated  liquor  is  again  used  in  the  washer,  and  by  its 
continuous  circulation  the  ammonium  salts  increase  in  quantity  until  eventually 
crystals-  are  deposited.  The  liquor  is  then  boiled,  the  sulphur  is  precipitated  and 
filtered  out,  and  the  remaining  liquor  is  evaporated  in  a  vacuum  boiler,  producing 
crystals  of  sulphate  of  ammonia— (NH4)2S406  =  (NH4)2S04  +  SO 2  +  28.  The 
sulphur  dioxide  evolved  is  used  for  regeneration  purposes.  In  addition  to  the 
equation  given  above  for  the  reaction  of  the-  polythionate  in  the  ammonia  washer, 
the  following  reaction  also  occurs  — 

(NH4)2S406  +  3H2S  =  (NH4)2S203  +  58  +  3H20 


SEMI-DIKECT  PROCESSES 

These  processes,  although,  scientifically,  not  so  perfect  as  those  discussed  above, 
in  view  of  the  necessity  for  introducing  sulphuric  acid,  are  undoubtedly  more  desir- 
able, owing  to  the  ease  with  which  they  may  be  operated  in  practice.  When  plants 
of  this  description  are  employed,  the  ordinary  washing  and  scrubbing  apparatus 
is  dispensed  with — 'the  ammonia  being  removed  by  bubbling  the  gas  through  a 
seal  of  sulphuric  acid.  The  chief  points  requiring  attention  in  order  to  make  the 

1     See  Journal  of  Gas  Lighting,  vol.  cvii.  p.  816  ;  also  Gas  World,  vol.  Ivii.  p.  250. 


THE  PRELIMINARY  PURIFICATION   OF  COAL   GAS     365 


process  a  success  are 
the  entire  elimina- 
tion of  all  tarry  mat- 
ter from  the  gas  and 
the  maintenance  of 
the  acid  bath  at  such 
a  temperature  as  to 
allow  of  the  forma- 
tion of  the  salt. 

The  K  o  p  p  e  r  s 
system  of  semi- direct 
recovery  is  shown 
diagrammatically  in 
Fig.  253.  The  hot 
gas  coming  direct 
from  the  ovens  enters 
the  coolers  or  con- 
densers, where  it  is 
reduced  in  tempera- 
ture to  about  75° 
Fahr.  The  gas  then 
passes  to  the  ex- 
hauster and  is  taken 
through  a  tar  ex- 
tractor  of  some 
efficient  type.  After 
the  tar  has  been  re- 
moved, the  gas  is  led 
through  the  re-heater, 
where,  by  means  of 
exhaust  steam,  its 
temperature  is  raised 
to  about  130°  Fahr. 
The  heated  gas  then 
passes  to  the  satura- 
tor,  where  the 
ammonia  is  recovered 
from  it  by  absorption 
in  sulphuric  acid. 
The  sulphate  as  it  is 
formed  falls  to  the 
bottom  of  the  vessel 
and  is  •continuously 
removed  4by  means  of  a  steam  or  compressed  air  ejector.  Finally,  the  sulphate  is 


366  MODERN   GASWORKS    PRACTICE 

delivered  to  a  centrifugal  drying  machine,  in  which  the  mother  liquor  is  removed 
from  it.  The  condensate  thrown  down  in  the  coolers,  also  the  overflow  products 
from  the  tar  extractor,  are  run  to  the  separating  tank,  which  is  so  arranged  that 
tar  and  liquor  can  separate,  owing  to  the  difference  in  their  specific  gravities.  The  two 
products  then  flow  into  their  respective  storage  tanks.  The  virgin  liquor  is  finally 
pumpsd  up  into  the  amm3nia  still,  where  it  is  heated  with  steam  and  lime  in  the 
usual  way.  The  ammonia,  sulphuretted  hydrogen,  and  carbon  dioxide,  resulting 
from  the  distillation  of  the  liquor,  are  then  admitted  to  the  crude  gas  main  at 
a  point  just  preceding  the  saturator. 


CHAPTER   XV 
THE  RECOVERY  OF  CYANOGEN 

THE  presence  of  hydrocyanic  acid  amongst  the  products  of  the  distillation  of  coal 
has  been  recognized  for  a  number  of  years,  and  many  and  varied  attempts  have  been 
made  to  effect  its  recovery  on  profitable  lines.  The  amount  of  hydrocyanic  acid 
occurring  under  normal  conditions  is,  however,  comparatively  small,  so  that  in 
many  cases  the  working  expenses  of  the  process  adopted  have  rendered  recovery 
unprofitable,  except  in  the  case  of  the  largest  concerns.  From  a  commercial  point 
of  view,  cyanogen  derives  its  value  from  the  fact  that  the  principal  method  of  treat- 
ing rocks  and  quartz  for  the  recovery  of  gold  is  by  the  cyanide  process,  with  or  with- 
out amalgamation  on  copper  plates.  The  rationale  of  the  process  is  the  crushing 
of  the  gold-bearing  rock  in  a  suitable  machine,  the  admixture  of  the  fines  with  water, 
so  as  to  form  a  sludge,  and,  finally,  the  passing  of  this  sludge  over  copper  plates 
amalgamated  with  mercury.  The  fine  gold  then  commixes  with  the  mercury,  whilst 
the  residue  of  crushed  ore  flows  away.  The  waste  is  known  as  "  tailings."  Periodic- 
ally, that  is  after  every  three  or  four  weeks,  the  copper  plates  are  scraped,  and  the 
amalgam  obtained  is  distilled  in  a  retort,  whence  the  mercury  is  evolved  and  the 
gold  left  behind.  The  mercury  treatment  is  still  employed  in  conjunction  with 
cyanide,  although  in  many  cases  the  ore  is  treated  direct  and  the  amalgamation 
process  is  dispensed  with.  To-day,  the  greater  portion  of  the  gold  output  of  the 
world  is  obtained  by  means  of  the  cyanide  method.  Briefly,  the  process  consists 
of  two  essential  parts : — 

(a)  Dissolving  the  gold  from  the  ore  in  a  cyanide  solution. 
(6)  Precipitation  of  the  gold  from  the  solution. 

The  mineral  as  won  from  the  mines  is  primarily  subjected  to  several  sortings, 
and  is  then  treated  in  large  vats  with  a  solution  of  sodium,  or  occasionally  potas- 
sium, cyanide.  An  extremely  weak  solution  is  usually  employed,  owing  to  the  fact 
that  the  greater  the  percentage  strength  of  the  cyanide  the  more  easily  are  metals 
other  than  gold  dissolved.  The  period  of  treatment  generally  varies  from  twelve 
to  twenty- four  hours,  and  in  cases  where  the  mineral  may  require  extended  contact 
the  cyanide  solution  should  be  renewed  every  three  or  four  days.  Precipitation  of 
the  gold  from  the  cyanide  solution  is  usually  carried  out  by  means  of  zinc,  the  latter 
displacing  the  gold  from  the  cyanide  as  follows : — 

2NaAu(CN)  2+Zn  =Na  2Zn(CN)4+2Au. 

367 


368  MODERN   GASWORKS   PRACTICE 

The  process,  however,  is  not  so  simple  as  might  be  supposed  from  the  above 
brief  outline,  and  many  modifications  have  been  introduced  from  time  to  time  with 
the  object  of  rendering  the  work  more  economical  and  of  increasing  the  efficiency 
of  recovery.  In  addition  to  being  employed  for  the  treatment  of  gold-bearing 
ores,  cyanides  find  a  limited  use  in  the  manufacture  of  dyes  and  paints,  and  in  electro- 
plating. 

CYANOGEN  IN  COAL  GAS 

The  cyanogen  in  coal  gas  is  almost  wholly  in  the  form  of  hydrocyanic  acid, 
although  some  authorities  say  that  it  is  also  present  as  free  cyanogen  and  ammonium 
cyanide.  Hydrocyanic  acid  is  produced  by  the  combination  of  hydrogen,  carbon, 
and  nitrogen  at  high  temperatures  in  the  retort,  and  makes  its  appearance  among 
the  products  at  temperatures  considerably  higher  than  those  at  which  ammonia  is 
at  a  maximum  (1,OCO°  Fahr.).  It  is  probable  that  a  portion  of  the  ammonia  itself 
is  split  up  into  its  elements,  hydrogen  and  nitrogen,  these  re-combining,  with  the 
addition  of  the  carbon  atom,  to  form  hydrocyanic  acid  (HCN).  As  regards  the 
original  nitrogen  in  coal,  it  has  been  shown  that  less  than  2  per  cent,  of  this  goes 
to  form  cyanogen,  the  quantity  of  the  latter  considerably  increasing  when  high  and 
extreme  temperatures  of  distillation  are  employed  (  seepage  257).  The  most 
favourable  temperature  in  the  retorts  for  the  formation  of  cyanogen  is  said  to  be 
2,2CO°  Fahr.,  and  the  maximum  amount  recoverable  from  a  ton  of  English  coal 
is  about  1£  Ib.  of  hydrocyanic  acid,  or  about  10,000  grains. 

Cyanogen  compounds  may  be  found : — 

(a)  In  the  gas,  chiefly  as  hydrocyanic  acid. 

(b)  In  the  ammoniacal  liquor,  mainly  as  ammonium  cyanide,  ferrocyanides, 
and  sulphocyanide. 

(c)  In  spent  oxide,  chiefly  as  "  Prussian  blue  "  (ferric-ferrocyanide). 

(d)  In  spent  lime,  as  calcium  sulphocyanide,  and  to  some  extent  as  calcium 
ferrocyanide. 

(e)  In  spent  liquor  from  the  sulphate  plant,  as  ferrocyanide  compounds. 

The  chief  processes  nowadays,  in  this  country  at  any  rate,  are  those  by  means  of 
which  the  cyanogen  is  extracted  from  the  gas  and  recovered  as  either  (a)  ammonium 
sulphocyanide  (NH4SCN)  or  sodium  ferrocyanide  (prussiate  of  soda,  Na4FeC6N6). 
Ultimately  the  sulphocyanide  or  prussiate  is  converted  into  sodium  cyanide  for 
gold  working  processes ;  and,  so  far  as  this  operation  is  concerned,  recovery  as 
prussiate  is  to  be  preferred. 

Per  se,  the  extraction  of  cyanogen  as  a  distinct  by-product  will,  in  normal  times, 
only  prove  profitable  in  the  case  of  the  larger  gasworks.  Indirectly,  however, 
the  removal  of  the  compound  from  the  gas  presents  many  advantages,  and  if  it 
could  be  generally  extracted  and  turned  to  profitable  account  the  task  of  the  gas 
engineer  would  certainly  be  made  easier.  Apart  from  the  fouling  of  gasholder 
water,  and  the  possible  corrosion  of  gasholder  plates  and  other  apparatus,  the  re- 
moval of  the  cyanogen  is  strongly  to  be  urged,  owing  to  its  effect  on  the  effici- 


THE  RECOVERY  OF  CYANOGEN        369 

ency  of  the  present-day  purifying  material.  It  is  beyond  all  question  that  oxide 
of  iron,  whether  natural  or  artificial,  will  remain  in  an  active  condition  for  a  much 
greater  length  of  time  when  the  cyanogen  is  absent.  Both  Bueb  and  Guillet 
have  shown  that  in  some  cases  the  efficiency  of  the  "  dry  "  purifiers  may  be  increased 
by  so  much  as  50  per  cent,  if  the  compound  is  extracted.  Perthuis  has  pointed 
out  that  in  certain  circumstances  cyanogen  is  responsible  for  a  reaction — not  wholly 
understood — in  the  purifiers  which  may  cause  the  material  in  them  actually  to 
increase  the  sulphur  impurities  in  the  gas. 

On  works  where  no  recovery  plant  for  cyanogen  is  in  use  the  bulk  of  the 
substance  will  be  removed  by  the  oxide  or  lime  purifiers,  although  some  slight  reduc^ 
tion  will  take  place  during  the  passage  of  the  gas  through  the  wet  purification  plant.. 
No  definite  statement  can  be  made  as  to  the  amount  of  cyanogen  which  will  pass 
through  the  oxide  boxes.  In  many  works  the  gas  at  the  outlet  of  the  purifiers  shows 
only  a  trace,  while  in  other  cases  as  much  as  8  to  10  grains  of  hydrocyanic  acid  per 
100  cubic  feet  of  gas  will  be  found.  The  cyanogen,  by  combining  with  the  iron 
salts,  is  absorbed  in  the  purifiers  as  ferrocyanides.  In  this  way  a  portion  of  the 
active  material  is  rendered  inert  so  far  as  the  absorption  of  sulphuretted  hydrogen, 
is  concerned.  The  Prussian  blue,  moreover,  by  coating  the  granules  of  the  oxide,, 
exerts  an  effect  far  greater  in  proportion  than  the  actual  extent  in  which  it  is  present. 
Spent  oxide  with  a  content  of  25  per  cent,  of  sulphur  has  been  found  to  contain  as 
much  as  12  \  per  cent,  of  Prussian  blue,  although  in  normal  cases  the  amount  of  the 
latter  present  will  not  exceed  \\  per  cent.  As  regards  the  formation  of  Prussians 
blue  in  the  purifying  boxes  the  reactions  taking  place  are  by  no  means  simple,  and 
there  seems  little  doubt  that  the  ferric-ferrocyanide  is  the  result  of  oxidation  of  a 
ferrous  cyanide  which  is  formed  in  the  first  instance.  Thus  the  hydrocyanic  acid 
reacts  with  the  oxide  of  iron  : — 

Fe203+4HCN=2Fe(CN)2  (ferrous  cyanide) +2H20+0,  and  by  oxidation  gives  :— 
18Fe(CN)2  +  302=2Fe203+2Fe4,3Fe(CN)6  (Prussian  blue). 

Many  different  opinions  have  been  expressed  as  to  the  probable  reactions  account- 
ing for  the  Prussian  blue,  and  although  the  above  seems  reliable,  it  is  open  to  some 
questioning.  Again,  there  is  a  likelihood  that  the  hydrocyanic  acid  does  not  react 
with  the  active  material  (Fe203),  but  with  the  iron  sulphide,  and  the  experiments 
of  Leybold  would  appear  to  corroborate  this.  The  mode  of  reaction  in  this  case 
would  then  be  : — 

FeS+2HCN=SH2+Fe(CN)2 

The  ferrous  cyanide  is  finally  oxidized  to  ferric-ferrocyanide  as  shown  above.. 
The  chief  point  to  notice  is  that  moisture  or  the  admission  of  steam  to  the  boxes 
will  aid  the  formation  of  Prussian  blue  whilst  ammonia  will  prevent  it.  The  pres- 
ence of  ammonia  in  the  crude  gas,  therefore,  greatly  facilitates  the  formation  of 
sulphocyanides  and  on  this  account  is  desirable.  The  sulphocyanides  formed,  being 
of  a  soluble  nature,  are,  accordingly,  run  off  from  the  material  through  the  drain- 
pipes of  the  purifier  and  do  not  form  a  film  on  the  granules  of  oxide  as  is  the  case 
with  the  ferrocyanide.  The  action  of  the  ammonia  is  not  perfectly  clear,  and  it 

B  E 


370  MODERN   GASWORKS   PRACTICP: 

cannot  be  (as  so  often  stated)  that  it  combines  direct  with  the  hydrocyanic  acid 
and  sulphur  to  form  ammonium  sulphocyanide  as  in  the  polysulphide  process  (see  page 
372),  for  the  amount  of  ammonia  required  would  be  greatly  in  excess  of  that  actually 
present  in  the  gas  at  this  point.  It  is  well  known,  however,  that  the  formation  of 
Prussian  blue  cannot  take  place  when  alkaline  conditions  prevail,  so  that  if  a  small 
quantity  of  ammonia  (about  1  grain  per  ICO  cubic  feet)  is  allowed  to  travel  forward 
in  the  gas  from  the  scrubber  the  formation  of  Prussian  blue  in  any  quantity  will 
very  seldom  follow.  The  same  effect,  however,  is  not  seen  when  an  alkali  such  as 
lime  is  mixed  in  small  proportion  with  the  oxide  in  the  purifiers,  owing  to  the  lime 
being  quickly  carbonated  by  the  C02  coming  forward  with  the  gas. 


As  already  stated,  the  cyanogen  recovered  as  a  by-product  in  the  gasworks 
of  this  country  is,  without  exception,  removed  from  the  gas  alone.  On  the  Continent 
the  spent  oxide  is  more  frequently  treated  for  the  purpose ;  but,  in  general,  the 
class  of  coal  employed  gives  higher  yields  of  cyanogen  than  do  English  coals.  Of 
the  more  important  processes  which  have  been  adopted  in  this  country  the  followr- 
ing  may  be  mentioned,  although,  some  have  been  discarded  in  favour  of  more  modern 
methods  : — 

(a)  The  Foulis  process  (prussiate  of  soda). 

(6)  Wilton's  process  (prussiate  of  soda). 

(c)  The  British  Cyanides  Company's  process  (sulphocyanide). 

(d)  The  Davis-Neill  process  (prussiate  of  soda). 

(e)  The  polysulphide  process  (sulphocyanide). 

Other  processes  of  interest  are  those  of  Ciselet  and  Deguide,  and  of  the  South 
Metropolitan  Gas  Company  in  collaboration  with  the  Thann  Chemical  Manufacturing 
Company,  of  Alsace. 

THE  FOULIS  PROCESS 

The  Foulis  process  was  patented  in  1892  and  first  put  into  operation  at  the 
Glasgow  gasworks.  Chloride  of  iron  is  made  by  dissolving  scrap  iron  in  hydro- 
chloric acid  in  large  vats,  preferably  made  of  slate.  The  iron  chloride  is  then 
mixed  with  the  requisite  quantity  of  sodium  carbonate  so  that  iron  carbonate 
results — 

FeCl2+Na2C03=FeC03+2NaCl. 

The  iron  carbonate  is  precipitated  and  the  sodium  chloride  is  run  to  waste. 
The  iron  carbonate  is  then  removed  to  a  further  tank,  where  it  is  mixed  with  more 
sodium  carbonate  in  the  necessary  theoretical  quantities.  The  tank  is  provided  -.vith 
a  stirrer  and  has  an  outlet  leading  into  the  first  bay  of  a  suitable  washer-scrubber. 
The  mixture  is  run  direct  into  the  washer  and,  combining  with  the  hydrocyanic 
acid  in  the  gas,  is  converted  into  sodium  ferrocyanide,  which  is  run  away  from  the 
final  bay  as  quickly  as  it  is  produced— 

FeC03+2Na2C03+6HCN. 

=Na4Fe(CN) ,  (sodium  ferrocyanide)+3C02+3H20 


THE  RECOVERY  OF  CYANOGEN        371 

The  crude  ferrocyanide  is  evaporated  nearly  to  dryness  in  pans,  and  when 
cool — an(i)  consequently,  solid — it  is  wheeled  to  the  stores.  In  this  condition  it 
contains  about  75  per  cent,  of  sodium  ferrocyanide.  Oxidation  of  the  FeC03 
can  be  prevented  by  mixing  in  one  bay  of  the  washer-scrubber  and  by  adding 
the  whole  of  the  sodium  carbonate  at  one  time. 

WILTON'S  PROCESS 

In  Wilton's  process  cyanogen  is  arrested  in  the  process  of  scrubbing  by  adding 
to  the  rotary  washer-scrubber  an  iron  salt.  It  is  more  or  less  essential  that  the 
liquor  in  the  washer- scrubber  should  be  strong,  i.e.  about  16  oz.,  otherwise  the 
whole  of  the  hydrocyanic  acid  will  not  be  arrested.  Ammonium  ferrocyanide  is 
formed  as  follows  : — 

FeS04+6HCN+6NH4OH=(NH4)4Fe(CN)6+(NH4)2S04+6H20 

and  is  afterwards  converted  into  Prussian  blue  by  the  addition  of  a  further  quantity 
of  iron — 

3(NH4^4Fe(CN)6+2Fe2(S04)3=Fe4,3Fe(CN)6+6(NH4)2S04. 

BRITISH  CYANIDES  COMPANY'S  PROCESS 

The  process  of  the  British  Cyanides  Company,  of  Oldbury,  recovers  the  hydro- 
cyanic acid  in  the  form  of  a  sulphocyanide.  The  method  consists  essentially  of 
the  preparation  of  a  solution  containing  ammonium  polysulphide  by  the  addition 
of  coarsely  powdered  sulphur  to  ordinary  ammoniacal  liquor.  A  rotary  washer- 
scrubber,  usually  of  the  Holmes  type  (see  page  343)  is  employed  for  bringing  gas 
and  liquor  in  through  contact,  and  the  top  of  each  bay  is  provided  with  a  cup-shaped 
receiver  having  a  closely  fitting  lid.  These  cups  are  periodically  filled  with  the 
powdered  sulphur,  and  the  ammonium  sulphide  in  the  liquor  combines  with  the 
free  sulphur  added  to  give  ammonium  polysulphides,  (NH4)  2S2  to  (NH4)2S5.  The 
process  is  dependent  upon  the  fact  that  whereas  hydrocyanic  acid  will  combine  with 
ammonium  polysulphide,  it  will  not  enter  into  action  with  ammonium  sulphide.  Am- 
monium sulphocyanide  is  formed  in  the  washer,  the  liquor  flowing  out  with  a  strength 
varying  from  15°  to  20°  Twaddel.  With  the  disulphide  the  equation  of  the  reaction 
occurring  is  as  follows — 

(NH4)2S2+HCN=NH4SCN+NH4HS. 

Whilst  the  plant  is  in  operation  it  is  usual  to  test  the  liquor  in  the  various  bays 
of  the  washer-scrubber  from  time  to  time  in  order  to  ensure  that  it  consists  of  am- 
monium polysulphide  and  not  the  sulphide.  This  may  be  done  by  adding  a  small 
quantity  of  acid  to  the  liquor,  when  a  decided  precipitate  of  sulphur  will  be  given 
if  the  polysulphide  is  present,  whilst  the  sulphide  will  give  practically  no  precipitate 
at  all.  In  this  system  the  hydrocyanic  acid  is  extracted  before  the  ammonia  has 
been  removed  from  the  gas,  as  in  this  way  the  proportion  of  ammonium  sulphide 
is  increased  and  the  efficiency  of  extraction  rendered  higher.  To  this  end  the 
plant  is  usually  placed  immediately  after  the  exhausters,  with  some  efficient  form 
of  tar  extractor  coupled  up  to  its  inlet. 


372  MODERN   GASWORKS   PRACTICE 

It  is  found  that  by  the  British  Cyanides  process  practically  the  whole  of  the 
hydrocyanic  acid  is  removed  from  the  gas,  and  the  liquor  may  be  readily  worked 
up  to  a  strength  of  from  3  to  4  Ib.  of  ammonium  sulphocyanide  per  gallon.  As 
regards  ammonia,  the  strength  of  the  liquor  may  be  as  high  as  40  oz.,  but  90  per 
cent,  of  the  ammonia  is  present  in  the  "  fixed  "  state.  In  the  case  of  some  works 
the  liquor  is  passed  on  to  the  sulphate  plant  and  treated  for  the  recovery  of  ammonia 
in  the  ordinary  way,  by  the  addition  of  lime.  The  lime  then  takes  the  place  of  the 
ammonia  and  gives  rise  to  calcium  sulphocyanide,  which  may  be  sold  direct  to  the 
cyanide  agents,  by  whom  it  is  converted  into  sodium  cyanide.  The  conversion 
of  ammonia  into  calcium  sulphocyanide  takes  place  'as  follows : — 

2(NH4SCN)+Ca(OH)2=Ca(SCN)2+2NH4OH. 

It  has  been  found  that  in  addition  to  absorbing  hydrocyanic  acid  some  reduc- 
tion of  the  carbon  disulphide  in  the  gas  may  take  place  as  the  gas  travels 
through  the  plant.  But  whilst  in  some  cases  so  much  as  20  to  25  grains  of  CS2 
per  100  cubic  feet  was  absorbed,  at  other  times  a  reduction  of  only  1  to  2  grains 
was  shown.  No  reliance  can  be  placed  upon  the  apparatus  for  this  purpose.  Col- 
man,  however,  in  a  series  of  experiments,  found  that  in  no  case  was  the  CS2  increased 
during  the  passage  of  the  gas  through  the  washer,  and  an  average  reduction  of  10 
grains  resulted  from  tests  extending  over  some  period.  The  exact  manner  in  which 
the  CS2  is  absorbed  is  not  perfectly  clear,  but  it  may  unite  with  the  ammonium 
sulphide  to  give  ammonium  thiocarbonate  (see  page  331)  as  follows — 

(NH4)2S+CS2=(NH4)2CS3. 

The  carbonic  acid  in  the  gas  is  prejudicial  to  the  absorption  of  CS2,  for  it  reacts 
with  thiocarbonate  and  drives  the  CS2  out  of  its  combination.  When  the  C02  con- 
tent in  the  gas  is  low  the  efficiency  of  CS2  absorption  should,  therefore,  be  increased. 
The  ammonium  thiocarbonate  gradually  becomes  converted  into  ammonium  sulpho- 
cyanide in  the  washer — 

(NH4)2CS3=NH4CNS+2H2S, 

so  that  in  this  way  the  carbon  disulphide  removed  is  turned  to  useful  account. 

THE  POLYSULPHIDE  PKOCESS 

The  British  Cyanides  Company  are  now  giving  up  this  process  and 
substituting  a  more  efficient  and  economical  method,  known  as  the  polysul- 
phide  process.  In  the  newer  process  the  hydrocyanic  acid  is  recovered  in  the 
form  of  ammonium  sulphocyanide,  but  the  necessity  of  introducing  a  special 
supply  of  free  sulphur  is  obviated  by  making  use  of  the  sulphur  in  spent 
oxide  for  the  production  of  the  polysulphides.  A  diagrammatic  sketch  of 
the  apparatus  is  shown  in  Fig.  254.  From  this  it  will  be  seen  that  the  vessel 
employed  resembles  an  ordinary  dry  purifier,  access  to  which  is  obtained  through 
portions  of  the  top  which  are  made  removable  on  the  lines  of  a  Green's 
purifier.  The  inlet  gas  entering  at  the  base  of  the  vessel  passes  in  the  first 
instance  through  a  tar  extractor  operated  on  the  bubbling  principle,  the  gas  passirg 


THE   RECOVERY   OF   CYANOGEN 


373 


through  the  cyanide  liquor  which  forms  the  seal.  Above  the  tar  extractor  is  arranged, 
on  suitable  brackets,  a  tier  of  ordinary  wooden  purifier  grids  which  support  a  layer 
of  spent  oxide,  evenly  spread  over  the  whole  cross-section  of  the  vessel,  and  about 


FIG.  254. — THE  POLYSULPHIDE  PLANT. 

24  inches  in  depth.  The  spent  oxide  used  should  preferably  be  of  good  quality, 
containing  not  less  than  50  per  cent,  of  sulphur.  It  is  kept  in  a  moist  condition 
by  a  simple  arrangement  of  sprays  fitted  around  the  four  sides  of  the  vessel  at  a 
point  well  above  the 
oxide  level.  These  sprays 
may  be  seen  in  Fig.  255, 
which  shows  a  complete 
section  of  the  box  with 
the  two  inlets  and  out- 
lets for  the  gas.  A 
short  period  of  spraying 
every  day  with  water  or 
a  weak  cyanide  liquor  is 
all  that  is  necessary.  In 
this  way  the  polysulphide 
solution  is  formed  within  FIG.  255.  . 

the    interstices    of     the 

oxide  bed,  and  is  immediately  converted  into  ammonium  sulphocyanide  by  the 
incoming  gas.  The  cyanide  liquor,  after  trickling  through  the  oxide  mass,  drops 
to  the  base  of  the  vessel,  from  which  it  overflows  to  the  storage  tank  by  way 


-$-            -sf-           -®-           -<$>-     [    -®- 

.  Spent 

Tar 
Extrac 

•'•' 

L"**-" 

;:^U.:-"'l-i'>'-J'-i/J^;Cl-^ 

t 

lit 

m  .  .  _..._ 

4- 

m 

374  MODERN   GASWORKS   PRACTICE 

of  a  seal.     With  regard  to  the  actual  formation  of  the  sulphocyanide  it  would  seem 
that  a  straightforward  reaction  on  the  following  lines  takes  place — 

(NH4)2S2  (ammonium  polysulphide) +HCN=NH4SCN+NH4.SH. 
There  is,  however,  some  probability  that  a  portion  of  the  sulphocyanide  is 
formed  in  two  stages,  with  the  intermediate  production  of  thiocyanic  acid.     Thus 
ammonium  polysulphide  gives  ammonium  sulphide  and  thiocyanic  acid  as  follows- — 

(1)  (NH4)2S2+HCN=(NH4)2S+HSCN  (thiocyanic  acid). 

The  last-named  then  combines  with  more  ammonia,  in  the  form  of  the  hydrate, 
to  give  the  sulphocyanide — 

(2)  HSCN+NH4OH=NH4SCN+H20. 

Probably  the  most  surprising  feature  of  the  polysulphide  process  lies  in  the  fact 
that  although  sulphur  is  inevitably  required  for  the  completion  of  the  reaction,  the 
spent  oxide,  after  working  for  some  period,  shows  no  loss  in  sulphur  content,  and 
occasionally  some  increase  is  found.  It  would  seem,  then,  that  there  is  a  simul- 
taneous absorption  of  ammonia,  sulphuretted  hydrogen,  and  oxygen,  and  that — 
as  the  oxide  takes  up  SH2,  which  is  eventually  oxidized  to  sulphur — a  continuous 
supply  of  free  sulphur  is  automatically  provided.  The  process  would,  in  fact,  be 
continuous  but  that  the  physical  condition  of  the  spent  oxide  necessitates  periodical 
removal  from  the  vessel  and  the  substitution  of  a  fresh  layer.  The  period  for  which 
the  material  will  remain  in  action  varies  under  normal  conditions  between  three 
and  six  months.  Six  vessels  now  in  operation  at  one  gasworks  have  shown 
themselves  capable  of  extracting  practically  the  whole  of  the  hydrocyanic  acid 
over  a  period  of  six  months  without  requiring  remaking.  The  cyanide  boxes 
are  usually  made  either  20  or  25  feet  square  by  6  feet  deep.  The  former  size  is 
capable  of  dealing  effectively  with  1|  million  cubic  feet  of  gas  per  diem,  whilst  the 
latter  will  take  up  to  2  million  cubic  feet.  For  larger  volumes  of  gas  the  boxes 
are  operated  in  parallel,  although,  when  possible,  it  is  preferable  to  arrange  for 
two  purifiers  to  be  worked  in  series,  so  that  the  gas  travels  upwards  through  one 
and  downwards  through  the  second. 

Figures  obtained  in  actual  practice  show  that  one  ton  of  spent  oxide  is 
capable  of  removing  the  whole  of  the  cyanide  from  350  tons  of  coal.  One  of  the 
chief  recommendations  of  the  method  is  the  manner  in  which  the  duties  of  washers, 
scrubbers,  and  dry  purifiers  are  lightened.  Of  the  ammonia  contained  in  the  crude 
gas  entering  the  plant  an  average  of  from  30  to  35  per  cent,  is  absorbed,  the  sul- 
phuretted hydrogen  shows  a  reduction  of  35  per  cent.,  whilst  carbon  dioxide  falls 
off  by  from  5  to  12  per  cent.  No  claim  can  be  made  for  the  absorption  of  carbon 
disulphide.  It  is  essential  to  remember  that  there  must  be  a  small  proportion 
of  oxygen  in  the  inlet  gas.  In  general,  this  proportion  varies  between  0-2  to  C-6 
per  cent.  ;  and — by  oxidizing  the  iron  sulphides  in  the  purifier — gives  rise  to  the 
free  sulphur  which  is  vital  to  the  effective  working  of  the  process.  The  cyanide 
liquor  flowing  away  from  the  plant  varies  in  strength  from  2J  to  3  Ib.  of  ammonium 
sulphocyanide  per  gallon,  and  (after  conversion  to  calcium  sulphocyanide)  it  may 
be  concentrated  to  any  desired  strength. 


THE  RECOVERY  OF  CYANOGEN 


375 


THE  DAVIS-NEILL  PRUSSIATE  PROCESS 

The  Davis-Neill  process  is  one  of  com- 
paratively recent  introduction,  and  is  in 
operation,  notably,  at  the  Lin'acre  works  of 
the  Liverpool  Gas  Company.  The  hydro- 
cyanic acid  is  extracted  from  the  gas  by 
washing  with  a  solution  of  ferrous  carbonate 
and  soda.  The  first  step  in  the  process  is  the 
preparation  of  the  ferrous  carbonate,  which  is 
made  by  mixing  copperas  (sulphate  of  iron) 
with  ordinary  soda  ash  (carbonate  of  soda) — 
FeS04+Na2C03=FeC03+Na2S04. 

The  mixture  of  ferrous  carbonate  and 
sodium  sulphate  is  then  passed  through  the 
first  filter-press,  in  which  the  ferrous  carbon- 
ate is  retained  as  cakes.  After  thorough 
washing  with  clean  water  the  cakes  are  re- 
moved to  a  second  mixing  tank  or  agitator, 
where  they  are  intermixed  with  a  further 
quantity  of  soda  ash.  The  resulting  cream  is 
then  run  into  the  first  bay  of  any  suitable 
washer- scrubber.  On  meeting  with  the  gas  the 
iron  carbonate  is  converted  into  sulphide  by 
the  action  of  the  sulphuretted  hydrogen  in  the 
crude  gas,  whilst  the  hydrocyanic  acid  combines 
with  the  sulphide  in  the  presence  of  sodium  car- 
bonate to  form  sodium  ferrocyanide — 

(a)  FeC03+SH2=FeS+C02+H20. 

(6)  FeS+2Na2C03+6HCN=Na4Fe(CN)6+ 
1^+2002+211,0. 

In  addition  to  sodium  ferrocyanide  cer- 
tain quantities  of  other  compounds,  such  as 
sodium  and  ammonium  ferrous-ferrocyanide, 
are  formed.  For  this  reason  the  liquor  under- 
goes further  treatment,  so  that  the  whole  of 
the  cyanide  may  be  recovered  as  a  soluble 
prussiate.  Leaving  the  washer-scrubber  the 
liquor  passes  through  a  preliminary  heater  and 
then  enters  a  still  in  which  it  meets  with  a 
strong  solution  of  caustic  soda.  In  this  way 
the  sodium  ferrous-ferrocyanide  is  converted 
into  sodium  ferrocyanide  as  required — 


Na2Fe2(CN)6+2NaOH=Na4Fe(CN)6+Fe(OH)2. 


376  MODERN   GASWORKS   PRACTICE 

The  liquor  obtained  is  then  pumped  through  filter-press  No.  2,  in  which  any 
mud  (chiefly  consisting  of  iron  sulphide)  is  retained.  The  cyanide  solution,  consist- 
ing in  the  main  of  prussiate  of  soda,  but  containing  a  small  proportion  of  carbonate 
of  soda,  is  then  passed  through  an  evaporator,  and  is  finally  recovered  as  yellow 
prussiate  crystals.  These  crystals  are  afterwards  washed  with  mother  liquor  from 
the  finished  crystallizing  tanks,  for  the  purpose  of  removing  any  impurities  such 
as  soda  and  sulphocyanides.  The  washed  crystals  are  then  treated  in  a  re-dissolver, 
where  the  liquor  they  form  is  boiled  for  about  15  hours,  before  being  run  ofi  to  the 
finished  crystallizing  tanks.  Slow  cooling  is  desirable  at  this  stage,  otherwise  small 
^crystals  will  be  formed. 

BUEB'S  PROCESS 

The  process  of  Dr.  J.  Bueb  is  one  which  has  been  used  fairly  widely,  particularly 
<t>n  the  Continent.  The  apparatus  made  use  of  is  a  washer-scrubber,  in  which  a 
solution  of  ferrous  sulphate  dissolved  in  ammoniacal  liquor  is  employed  for  washing 
the  gas.  The  sulphate  is  converted  into  iron  sulphide  by  the  sulphuretted  hydrogen 
in  -the  crude  gas — 

FeS04+H2S+2NH3=FeS+(NH4)2S04. 

'The  sulphide,  ammonia,  and  hydrocyanic  acid  then  combine  to  form — 
((a)  Ammonium  ferrocyanide — 

FeS+6NH3+6HCN=(NH4)4Fe;CN)6+(NH4)2S. 

<(&)  Cyanide  of  iron — 

FeS+2NH3+2HCN=Fe(CN)2+(NH4)2S. 

<(c)  Ammonium  ferrous-ferrocyanide — 

2FeS+6NH3+6HCN=(NH4)2Fe2(CN)6+2(NH4)2S. 

By  treating  with  lime  the  insoluble  ferrous-ferrocyanide  is  converted  into  a 
"soluble  calcium  ferrocyanide — 

(NH4)2Fe2(CN)6+2Ca(OH)2=2NH4OH+Ca2Fe(CN)6+Fe(OH)2. 

The  free  ammonia  may  then  be  distilled  off  by  means  of  steam  and  recovered, 
whilst  the  residual  liquor  is  mixed  with  the  required  quantity  of  sodium  carbonate 
or  hydrate,  when  sodium  ferrocyanide  results — 

Ca2Fe(CN)6+2Na2C03=Na4Fe(CN)6+2CaC03. 

Ciselet  and  Deguide,  in  their  process,  first  bring  the  gas  into  contact  with  ferric 
hydrate,  which  absorbs  the  sulphuretted  hydrogen  and  hydrocyanic  acid  in  the 
gas.  The  sulphur  and  cyanogen  are  precipitated  in  the  form  of  iron  sulphide  and 
iron  cyanide.  The  iron  sulphide  is  then  regenerated  to  the  hydrate  by  means  of  an 
air  blast,  the  sulphur  being  precipitated  in  the  free  form.  After  regeneration,  the 
ferric-hydrate  solution  is  treated  with  sulphuric  acid,  which  renders  the  iron  soluble 
whilst  the  sulphur  and  cyanogen  remain  insoluble.  The  two  last-named  can  then 
be  separated  with  an  alkaline  solution,  which  dissolves  the  cyanogen  compounds 


THE  RECOVERY  OF  CYANOGEN        377 

and  forms  alkaline  ferrocyanides.     Meanwhile,  the  free  sulphur  remains  insoluble 
and  can  be  filtered  out. 

SOUTH  METROPOLITAN  GAS  COMPANY'S  PROCESS 

The  South  Metropolitan  Gas  Company  have  introduced  a  process  by  means 
of  which  the  cyanogen  in  the  gas  is  recovered  as  hydrocyanic  acid.  The  crude  gas 
is  washed  with  a  solution  of  ferrous  sulphate,  the  resulting  liquor  being  treated 
with  an  ammonium  salt  and  boiled  with  lime,  so  that  a  double  cyanide — i  e.  calcium- 
ammonium  ferrocyanide,  Ca(NH4)2Fe(CN)6 — is  formed.  The  acid  radicle,  namely, 
the  hydrocyanic  acid  portion  of  the  salt,  is  unaffected  by  the  action  of  sulphuric 
acid,  whilst  the  remainder  is  converted  into  ferrous  ammonium  ferrocyanide  and 
calcium  sulphate.  In  this  way  a  means  is  provided  for  separating  out  the  cyanogen 
as  hydrocyanic  acid  and  recovering  it  as  such. 

EXTRACTION  FROM  SPENT  OXIDE 

It  has  already  been  pointed  out  that  when  no  special  means  is  provided  for 
the  recovery  of  cyanogen  from  the  gas  nearly  the  whole  of  it  is  arrested  by  the  oxide 
of  iron  in  the  dry  purifiers.  Owing  to  the  possibility  of  revivifying  the  iron  sulphide, 
and,  accordingly,  the  utilization  of  the  mass  over  and  over  again,  considerable 
quantities  of  cyanogen  may  have  been  collected  by  the  time  the  material  is  finally 
spent.  There  are  numerous  processes  for  the  recovery  of  cyanogen  from  oxide, 
but,  in  general,  they  may  be  classified  into  two  distinct  groups,  namely — 

(a)  Those  in  which  the  free  sulphur  is  first  extracted  by  means  of  some  solvent 
such  as  carbon  disulphide. 

(b)  Those  in  which  the  spent  material  is  straightway  treated  for  the  recovery 
of  the  cyanogen. 

The  processes  in  the  latter  group  are  those  chiefly  in  use,  and  consist,  in  the 
main,  of  the  lixiviation  of  the  material  for  the  removal  of  the  soluble  salts,  such 
as  ammonia  and  the  sulphocyanides.  The  insoluble  cyanide  salts  then  undergo 
treatment  to  convert  them  into  soluble  compounds,  and  finally  the  whole  of  the 
cyanogen  is  recovered  as  potassium  ferrocyanide. 

Lixiviation  of  the  material  is  carried  out  in  tanks  in  which,  by  any  suitable 
arrangement,  the  oxide  is  thoroughly  washed  with  water.  The  liquor  thus  obtained 
is  treated  in  the  ordinary  manner  with  lime  for  the  recovery  of  ammonia,  a  certain 
amount  of  calcium  sulphocyanide  being  formed  by  the  action  of  the  lime.  The 
next  stage  is  the  recovery  of  the  insoluble  ferrocyanides  by  treating  them  with  lime 
or  other  alkali.  This  process  is  now  frequently  carried  out  in  a  mechanical  stirr- 
ing apparatus.  The  material  is  led,  together  with  the  dilute  liquid  obtained  in 
the  first  stage  of  the  process,  into  a  boiler,  and  the  mass  is  heated  with  steam 
and  thoroughly  intermixed  by  means  of  the  stirring  apparatus.  The  sludge 
obtained  is  then  caused  to  flow  to  a  filter- press  in  which  the  cyanide  solution  is 
separated.  The  cakes  from  the  press  are  afterwards  thoroughly  pulverized  and 
sifted,  mixed  with  lime,  and  finally  treated  again  in  a  stirring  tank.  The  resultant 
liquor  contains  chiefly  calcium  ferrocyanide  and  some  calcium  sulphocyanide. 


378  MODERN   GASWORKS   PRACTICE 

The  next  step  is  to  precipitate  the  ferrocyanides  from  the  solution,  so  that 
they  may  be  recovered.  This  may  be  carried  out  in  several  ways,  that  is  by 
iron,  ammonia,  or  potassium  salts.  When  utilizing  ammonia  the  cyanide  solution 
is  treated  with  hydrochloric  acid,  the  acid  being  added  until  the  mixture  is  acid. 
In  this  way  a  double  salt,  calcium- ammonium  ferrocyanide,  is  obtained — 

Ca2Fe(CN)6+2NH4Cl=Ca(NH4)2Fe(CN)6+CaCl2. 

The  double  cyanide  may  then  be  admixed  with  a  further  quantity  of  lime, 
when  a  pure  calcium  ferrocyanide  results — 

Ca(NH4)2Fe(CN)6+Ca(OH)2=Ca2Fe(CN)6+2NH3+2H20. 

Finally,  the  calcium  ferrocyanide  may  be  converted  into  potassium  ferrocyanide. 
When  potassium  chloride  is  used  for  precipitation  a  double  salt  is  again  formed, 
in  the  first  instance — 

Ca2Fe(CN)6+2KCl=CaK2Fe(CN)6+CaCl2. 

This  salt  is  then  separated  by  filtration,  washed,  and  treated  with  potassium 
carbonate,  when  potassium  ferrocyanide  results— 

CaK2Fe(CN)6+K2CO-3=CaC03+K4Fe(CN)6. 

CONVERSION  OF   CYANIDES   INTO  AMMONIA 

Although  the  hydrocyanic  acid  in  coal  gas  may  now  be  recovered  by  com- 
paratively simple  means,  universal  extraction  is  not  altogether  possible,  owing  to 
the  limited  demand  for  the  product.  For  this  reason  renewed  attempts  have  been 
made  to  overcome  the  market  difficulty  by  converting  the  cyanogen  into  ammonia, 
for  which  there  is  always  a  steady  demand.  The  idea  is  by  no  means  novel,  for 
mention  is  made  of  the  process  in  scientific  literature  published  some  seventy-five 
years  ago,  whilst  a  patent  specification  for  another  means  was  filed  in  1882. 

As  regards  more  recent  investigation  into  the  possibility  of  converting  cyanides 
into  ammonia,  mention  must  first  be  made  of  the  work  of  Henri  Burgevin  and  Burk- 
heiser.  The  former  conducted  his  experiments  with  the  cyanide  compounds  present 
in  spent  purifying  material.  Ammonia  can  te  extracted  from  these  by  dry  dis- 
tillation, or  by  treatment  with  steam  under  pressure,  followed  by  the  use  of  alkalies, 
or  .by  employing  a  mixture  of  soda  and  lime.  Such  processes  are,  however,  unsatis- 
factory on  a  manufacturing  scale,  and  Burgevin  has  overcome  the  drawbacks  of 
using  a  costly  reagent,  soda ;  whilst  by  his  method  the  incomplete  nature  of  the 
reaction  is  avoided.  The  employment  of  lime  alone  is  sufficient,  while  a  recovery 
of  practically  the  whole  of  the  nitrogen  is  claimed.  According  to  the  patent  specifi- 
cation, when  cyanide  compounds  are  recovered  by  means  of  raw  purifying  material, 
the  latter  must  first  be  treated  with  some  suitable  solvent  (such  as  carbon  disul- 
phide)  in  order  to  ensure  complete  absence  of  free  sulphur.  The  residue  is  then 
thoroughly  intermixed  with  slaked  lime  in  the  correct  proportions,  and  the  two 
compounds  are  caused  to  react  at  red  heat.  The  reaction  is  entirely  completed 
at  this  temperature,  and  the  gaseous  mixture  liberated  will  consist  chiefly  of  free 
ammonia.  If  care  is  taken  to  see  that  the  mixture  is  homogeneous,  it  is  said  that 


THE  RECOVERY  OF  CYANOGEN        379 

at  least  95  per  cent,  of  the  original  nitrogen  in  the  cyanide  compounds  can  be  re- 
covered in  the  form  of  ammonia.  The  approximate  quantity  of  lime  required  for 
effecting  the  transformation  is  ten  times  (by  weight)  of  the  amount  of  nitrogen 
contained  in  the  original  material  to  be  treated ;  and  it  is  suggested  that 
the  ammonia  should  be  converted  into  ammonium  sulphate  by  passing  the  gas  through 
a  seal  of  sulphuric  acid.  The  method  also  allows  for  the  partial  conversion,  into 
ammonia  of  the  small  proportion  of  nitrogen  compounds,  other  than  cyanides, 
which  is  to  be  found  in  purifying  materials. 

The  most  recent  process,  which  is  based  on  original  lines,  is  that  of  the  South 
Metropolitan  Gas  Company.  Although  detailed  particulars  are  not  available,  it 
appears  to  consist  essentially  of  treating  the  recovered  compound  (in  the  form  of 
a  sulphocyanide)  with  an  excess  of  sulphuric  acid  at  some  definite  temperature, 
when  ammonia,  carbon  oxysulphide,  and  acid  sulphate  of  ammonia  should,  result. 

It  is  well  known  that  the  action  of  sulphuric  acid  upon  potassium  sulpho- 
cyanide gives  thiocyanic  acid  — 

KCNS+H2S04=HCNS+KHS04, 

the  latter  then  being  decomposed  by  water,  in  the  presence  of  an  excess  of  sulphuric 
acid,  into  carbon  oxysulphide  and  ammonia — 

HCNS+H20=NH3+COS, 

the  ammonia,  at  the  same  time,  combining  with  the  sulphuric  acid. 

In  the  case  of  ammonium  sulphocyanide,  the  two  reactions  would  be  very 
similar  in  character ;  ammonium  bisulphate  resulting  in  the  first  place — 

NH4SCN+H2S04=HCNS+NH4HS04. 

The  second  reaction  for  conversion  into  ammonia  is  then  similar  to  that  given 
above.  The  process  would  appear  to  be  somewhat  delicate,  owing  to  the  fact  that, 
if  the  working  temperature  is  carried  too  high,  the  cyanogen  is  likely  to  be  volatilized, 
and  lost  in  the  form  of  thiocyanic  acid.  Accordingly,  temperature  regulation  plays 
an  important  part ;  but,  working  under  good  conditions,  a  conversion  of  98  per 
cent,  of  the  total  nitrogen  into  ammonia  should  be  possible.  In  addition  to  carbon 
oxysulphide  being  evolved,  it  seems  probable  that  some  sulphuretted  hydrogen 
results  from  the  reaction.  This  is  most  likely,  owing  to  the  fact  that  carbon  oxy- 
sulphide is  freely  absorbed  by  ammonia,  and,  on  evaporation,  yields  sulphuretted 
hydrogen,  or  possibly  urea  (see  page  380).  It  is  feasible,  too,  that  a  portion  of 
the  carbon  oxysulphide  may  split  up  in  the  presence  of  water  and  steam,  and  yield 
carbon  dioxide  and  sulphuretted  hydrogen,  according  to  the  equation — 

COS+H20=C02+H2S. 

THE   LIME   METHOD 

A  second  successful  method  is  based  on  lines  somewhat  similar  to  those  of 
Burgevin,  and  is  particularly  applicable  in  cases  where  hydrocyanic  acid  is  recovered 
in  the  ammonium,  and  finally  calcium,  sulphocyanide  form,  as  is  the  case  in  the 


380  MODERN   GASWORKS   PRACTICE 

polysulphide  cyanide  process.  The  calcium  sulphocyanide  produced  is  first 
evaporated  to  dryness,  and  is  then  mixed  with  an  excess  of  slaked  lime,  and  sub- 
jected to  a  moderate  heat  of  not  less  than  1,CCO°  Fahr.  Under  the  influence  of  this 
temperature  the  cyanides  are  broken  up  in  the  presence  of  steam,  and  yield  ammonia 
and  carbon  oxysulphide.  The  ammonia  may  be  drawn  off  to  an  absorption  vessel 
containing  sulphuric  acid,  while  the  carbon  oxysulphide  will  be  mostly  removed 
by  the  excess  of  lime.  The  manner  in  which  the  lime  and  cyanide  are  admixed 
is  of  no  little  importance  for  the  effective  working  of  the  process.  With  regard 
to  the  actual  reactions  taking  place,  these  appear  to  be  on  lines  such  as  the 
following — 

(a)  Ca(CNS)8+Ca(OH)a+2H20=2NH8+COS+CaC03+CaS. 

The  precaution  is  taken  of  removing  the  carbon  oxysulphide  evolved  by  arranging 
for  a  layer  of  lime  2  or  3  inches  deep  to  be  placed  over  the  mixture  in  the  heating 
chamber.  The  carbon  oxysulphide  is  then  removed  as  follows  : — 

(6)  COS+2Ca(OH)2=CaS+CaC03+2H20. 

The  removal  of  the  carbon  oxysulphide  in  this  way  is  essential ;  for  ammonia  and  this 
compound  may  combine,  with  the  possible  formation  of  urea,  according  to  the 
following  equation : — 

COS+2NH3=H2S+CO(NH2)2. 

So  far  as  the  respective  merits  of  the  two  more  modern  processes  are  concerned, 
there  is  little  to  choose  between  them  on  the  ground  of  efficiency—  both  giving  a 
conversion  of  about  98  per  cent.  For  a  works  having  its  own  sulphuric  acid 
plant,  however,  or  in  cases  where  supplies  of  acid  can  be  readily  obtained,  the  sul- 
phuric acid  method  is  undoubtedly  to  be  preferred.  In  the  lime  method, 
use  might  conceivably  be  made  of  the  waste  heat  from  the  retort  benches,  or  one 
or  two  retorts  could  be  set  apart  for  the  special  cyanide  purpose.  Furthermore, 
if  it  was  not  desired  to  recover  the  evolved  ammonia  there  and  then,  it  could  be 
passed  into  the  foul  main  along  with  the  gas,  when,  by  absorption  of  sulphuretted 
hydrogen  and  carbonic  acid,  it  would  lighten  the  work  of  the  ordinary  purifying 
vessels. 

From  the  financial  standpoint  there  is  nothing  particularly  alluring  about  the 
conversion  of  cyanides  into  ammonia.  It  must  be  remembered,  however,  that 
the  indirect  advantages  accruing  from  the  employment  of  a  cyanogen  plant  are  the 
chief  recommendation  of  the  process.  As  before  stated,  the  universal  extraction 
of  cyanogen  is  scarcely  feasible  at  the  present  time,  owing  to  the  restricted  market 
for  this  residual,  and  the  growing  tendency  to  produce  it  by  other  means. 

So  far  as  the  polysulphide  process  is  concerned,  the  average  cost  of  recovery  is 
from  0-04d.  to  0-05rf.  per  lb.,  or  about  ^d.  per  ton  of  coal  carbonized.  Assuming  a 
yield  of  5  lb.  of  calcium  sulphocyanide  per  ton,  it  will  be  seen  that  if  this  sells  at 
Id.  per  lb.  the  net  profit  is  in  the  neighbourhood  of  4|rf.  per  ton  of  coal  carbonized. 
Then,  if  this  quantity  of  calcium  sulphocyanide  was  further  worked  up  into  ammonia, 
it  should  give  about  4|  lb.  of  sulphate  of  ammonia,  thus  increasing  the  total  yield 


THE  RECOVERY  OF  CYANOGEN        381 

of  sulphate  from  an  average  of  28  Ib.  per  ton  of  coal  to  32  J  Ib.  per  ton,  or  by  rather 
more  than  15  per  cent.  With  sulphate  selling  at  lid.  per  Ib.,  the  additional 
revenue  from  this  source  would  be  about  5%d.,  against  4frf.  for  cyanide. 


TESTING  COAL  GAS  FOR  CYANOGEN 

The  gas  to  be  tested  for  cyanogen  is  passed  through  two  wash-bottles  of  about 
250  to  300  c.c.  capacity,  each  containing  ICO  c.c.  of  ammonium  polysulphide  solu- 
tion (made  by  shaking  up  a  10  per  cent,  solution  of  ammonium  sulphide  with  pow- 
dered sulphur).  A  little  (say  10  grains)  of  powdered  sulphur  is  also  put  into  each 
wash-bottle,  to  ensure  the  presence  of  an  excess.  The  gas  should  be  passed  through 
the  wash-bottles  at  the  rate  of  about  2  cubic  feet  per  hour,  and  the  test  should,  pre- 
ferably, be  continued  for  sixteen  hours  or  more.  The  amount  of  gas  passed  should  be 
determined  by  a  small  meter.  At  the  conclusion  of  the  test,  the  contents  of  the  wash- 
bottles  are  transferred  to  a  litre  flask,  and,  with  the  washings  made  up  to  1,000  c.c., 
50  c.c.  (or  such  aliquot  portion  as  represents  from  1  to  2  cubic  feet  of  gas)  are  trans- 
ferred to  a  small  porcelain  basin,  and  evaporated  on  the  water-bath  down  to  about 
10  c.c.  Some  hot  water  and  a  little  moist  carbonate  of  lead  are  added  (to  remove 
all  sulphides),  and  the  whole  filtered.  The  filtrate  is  slightly  acidified  with  dilute 
sulphuric  acid,  a  solution  of  sulphurous  acid  added  until  the  liquor  smells  strongly  of 
SO  2,  and  then  a  weak  solution  of  pure  sulphate  of  copper  in  slight  excess,  the  whole 
heated  a  short  time  on  the  water-bath,  filtered  hot,  and  washed. 

The  filter  containing  the  cuprous  sulphocyanide  is  transferred  to  a  beaker  (pre- 
ferably the  one  in  which  the  precipitation  took  place,  as  small  portions  of  the  pre- 
cipitate may  be  adhering  to  the  glass).  From  25  to  50  c.c.  cf  normal  caustic  soda 
free  from  chlorides  are  added,  and  about  ICO  c.c.  of  boiling  water,  and  the  whole 
Iteated  on  the  water-bath,  with  frequent  stirring,  until  the  cuprous  oxide  beccmes 
sufficiently  granular  to  filter.  Filter  while  still  hot,  wash  well  with  hot  water,  and 
allow  the  combined  filtrate  and  washings  to  cool.  Acidify  slightly  with  pure  dilute 
nitric  acid,  add  a  few  drops  of  ferric  sulphate  solution,  and  titrate  with  decinormal 
silver  nitrate  until  the  colour  disappears.  Towards  the  end  of  the  titration  add  a 
few  more  drops  of  ferric  sulphate  to  increase  the  distinctness  of  the  end  reaction. 

Example.  23-5  cubic  feet  of  gas  were  passed  through  the  wash-bottles  in  twenty- 
four  hours,  and  the  contents  were  made  up  to  1,CCO  c.c.,  of  which  50  c.c.  (representing 
1-175  cubic  feet  of  gas)  were  taken.  After  proceeding  as  above  32-7  c.c.  of  deci- 
normal silver  nitrate  were  required  for  titration — 

1  c.c.  of  silver  nitrate  =  0-C076  gramme  of  ammonium  sulphccyanide. 
.'.32-7        „    '        „      =0-2485      „ 

i.e.  1-175  cubic  feet  of  gas  contain  C-2485  gramme  of  ammonium  sulpho- 
cyanide, 

or  ICO  cubic  feet  of  gas  contain  21-1  grammes  of  ammonium  sulphccyanide. 

There  are  15-43  grains  in  1  gramme,  therefore  21-1  x  15-43  =  325-5  grains  of 
ammonium  sulphocyanide  per  ICO  cubic  fp.et. 


382  MODERN  "GASWORKS   PRACTICE 

The  molecular  weight  of  ammonium  sulphocyanide  is  76,  and  that  of  hydrocyanic 

27 

acid  27,  so  that  325-5  X  —  =  115-6  grains  HCN  per  100  cubic  feet. 

76 

The  above  test  is  usually  made  use  of  only  when  sulphocyanide  processes  are 
in  operation.  When  ferrocyanide  plants  are  employed  the  following  method  is 
preferable — 

A  30  per  cent,  solution  of  caustic  soda  or  caustic  potash  is  mixed  with  a  12 
per  cent,  solution  of  ferrous  sulphate  in  the  proportion  of  5  to  1.  The  mixture  is 
poured  into  three  Woulfie's  bottles,  and  gas  is  passed  through  at  the  rate  of  1  cubic 
foot  per  hour.  After  about  10  cubic  feet  of  gas  have  been  passed  the  mixture  (col- 
lected from  the  three  WouliTe's  bottles)  is  washed  into  a  graduated  flask,  and  a 
portion  is  taken  for  analysis.  The  mixture  is  boiled  until  free  from  ammonia,  and 
is  then  filtered.  The  filter  paper  is  washed  with  hot  water  until  a  few  c.c.  on  being 
acidified  with  hydrochloric  acid  give  no  blue  colouration  on  the  addition  of  ferric 
chloride.  The  filtrate  and  washings  are  acidified  with  hydrochloric  acid  and  the 
cyanogen  is  precipitated  with  ferric  chloride,  as  Prussian  blue.  The  whole  is  then 
poured  into  a  tared  filter  paper  and  well  washed  with  hot  water  until  the  filtrate  is 
free  from  iron  salts.  The  filter  paper  and  contents  are  then  dried  and  weighed. 

Example. — 10  cubic  feet  of  gas  were  passed  through  the  caustic  soda  and  ferrous 
sulphate  mixture.  The  mixture  washings  were  then  made  up  to  500  c.c.,  of  which 
100  c.c.  were  taken  for  analysis,  i.e.  equal  to  2  cubic  feet  of  gas.  After  treatment 
the  amount  of  Prussian  blue  obtained  was  4  grains. 

860  parts  of  Prussian  blue  contain  468  parts  of  cyanogen  (CN) ;    therefore, 

4  x  468 
4  grains  will  contain  =2-18  grains  of  cyanogen  from  2   cubic  feet 

of  gas, 

or  2-18  x  50  grains  =  109  grains  per  100  cubic  feet  of  gas. 


CHAPTER   XVI 
THE  DRY  PURIFICATION  OF  COAL  GAS 

THE  theory  and  practice  of  the  dry  purification  of  coal  gas,  the  chemical  changes 
involved,  and  the  construction  and  working  of  the  necessary  apparatus  are  subjects 
which,  if  dealt  with  in  their  entirety,  would  justly  claim  a  complete  volume  to  them- 
selves. For  this  reason  it  is  impossible,  within  the  limits  of  a  single  chapter,  to  touch 
upon  more  than  the  salient  features  of  the  process  and  upon  those  sections  of  it  which 
are  of  direct  interest  to  the  gas  engineer. 

In  some  instances,  nowadays,  purification  is  carried  to  extreme  lengths,  in  order 
that  a  gas  of  exceptional  purity  may  be  supplied  to  the  consumer.  In  the  majority 
of  cases,  however,  the  gas  is  treated  in  such  a  manner  that  it  may  satisfy  the  usual 
statutory  requirements,  whilst  no  attempt  is  made  to  produce  a  super- quality. 

At  this  stage  of  the  manufacturing  process  the  impurities  present  in  the  gas 
may  be  set  down  as  follows — 


Ammonia       .          . 

Sulphuretted  hydrogen    . 

Sulphur  compounds  (other  than  SH2) 

Hydrocyanic  acid   . 

Carbon  dioxide 


nil  to  1-5  grains  per  100  cubic  feet. 
500  to  800      „ 

35  to  50 

50  to  70 
750  to  1,150  „ 


Of  these,  sulphuretted  hydrogen  must,  in  accordance  with  the  requirements  of  the 
law,  be  removed  to  the  merest  trace.  This,  however,  is  not  the  case  with  the 
remaining  four  compounds. 

Until  the  year  1905  a  certain  limit  was  placed  (in  London  and  many  provincial 
towns)  on  the  quantity  of  sulphur  compounds  present,  with  the  result  that  special 
treatment  was  accorded  the  gas  for  the  removal  of  these  compounds  before  it  left 
for  the  distribution  area.  The  limits  imposed  at  that  time  precluded,  during  the 
winter  months,  a  greater  quantity  of  sulphur  compounds  than  22  grains  per  ICO 
cubic  feet  of  gas,  whilst  during  the  summer  months  the  limit  was  reduced  to  17  grains. 
The  greater  portion  of  the  cyanogen  is  extracted  during  the  passage  of  the  gas  through 
the  oxide  purifiers,  unless,  of  course,  a  special  plant  for  its  recovery  has  been  previously 
interposed.  Carbon  dioxide,  as  previously  explained,  is  not  strictly  an  impurity  but 
a  diluent.  There  are  no  statutory  restrictions  as  to  its  presence  in  the  finished  gas, 
and  its  effect  is  chiefly  felt  in  the  direction  of  illuminating  and  calorific  power  tests 
(see  page  394). 

383 


384  MODERN   GASWORKS   PRACTICE 

Of   the  impurities  named,  the  gas  in  normal  instances    contains,  when  dis- 
•  tributed,  the  following  quantities — 

Sulphuretted  hydrogen          ....  nil. 

Ammonia    .......  nil. 

Sulphur  compounds  (other  than  SH2)  .          .  35  to  50  grains  per  100  cubic  feet. 

Hydrocyanic  acid         ,  nil  to  10          „  „  „         „ 

Carbon  dioxide    .          .          .          .          .          .  750  to  1,150  „  „  „         „ 

Where  a  proportion  of  carburetted  water  gas  is  added  to  the  coal  gas  the  mix- 
ture (owing  to  the  lower  sulphur  content  of  water  gas)  contains  a  smaller  percentage 
of  sulphur  impurities  than  does  a  neat  coal  gas.  Purified  carburetted  water  gas 
contains  on  an  average  from  10  to  15  grains  of  sulphur  compounds  per  100  cubic 
feet. 

The  abolition  of  the  sulphur  clauses  in  1905  did  much  to  simplify  the  process 
of  gas  purification,  in  that  lime  as  an  absorptive  medium  is  now  largely  dispensed 
with.  The  somewhat  erratic  operation  of  this  material  and  the  uncertainty  of  its 
working  were  such  as  to  prove  a  constant  anxiety  to  the  works  manager.  In 
addition,  considerable  expense  was  incurred  in  order  to  effect  the  removal  of  an 
impurity  present  in  quantities  so  small  as  to  render  it  practically  innocuous.  To-day 
oxide  purification  for  the  removal  of  sulphuretted  hydrogen  is  of  primary  interest 
to  the  gas  engineer,  although  the  use  of  lime  has  been  by  no  means  universally 
discarded. 

REMOVAL   OF   SULPHURETTED   HYDROGEN 

The  elimination  from  the  gas  of  this  impurity  presents  no  great  difficulties,  but 
the  manner  in  which  the  necessary  plant  is  operated  varies  considerably  with  the 
tastes  of  the  engineer.  Of  the  original  quantity  of  sulphuretted  hydrogen  the  bulk 
remains  in  the  gas  after  the  latter  has  passed  the  washers  and  scrubbers,  and  is  almost 
invariably  removed  by  causing  the  gas  to  pass  in  contact  with  layers  of  special 
material  in  a  moist  condition.  The  chief  materials  employed  for  sulphuretted 
hydrogen  removal  have,  in  the  past,  been  hydrated  lime,  hydrated  oxide  of  iron,  and 
manganese  dioxide  in  the  form  of  Weldon  mud.  Natural  ferric  oxide  (bog-ore)  is 
still  largely  made  use  of,  but  in  recent  years  there  has  been  a  tendency  to  turn  to 
various  artificial  preparations,  which  may  be  obtained  more  cheaply  and  which,  in 
many  cases,  have  increased  activity  as  compared  with  bog-ore. 

NATURAL  OXIDE  OF  IRON 

Natural  oxide  of  iron,  or  bog-ore,  occurs  in  peaty  deposits  in  large  quantities 
in  Ireland,  Holland,  and  Belgium,  also  to  a  limited  extent  in  England,  chiefly  in  the 
neighbourhood  of  Westbury  (Wiltshire).  In  its  natural  form  the  ore  contains  from 
50  to  60  per  cent,  of  water,  and  between  30  to  35  per  cent,  of  ferric  oxide  (Fe203). 
In  addition  to  iron  compounds  the  virgin  material  contains  about  15  to  25  per  cent, 
of  inert  matter,  consisting  chiefly  of  vegetable  substances  and  silica.  In  the  dried 
state  the  analysis  of  an  oxide  of  good  quality  will  vary  between  the  following  limits — 


THE   DRY   PURIFICATION   OF   COAL  GAS  385 

Hydrated  ferric  oxide  (Fe203,H2O) 60  to  65  per  cent. 

Organic  matter        .          .          ...          .          .          .          .  15  to  25        ,, 

Silica .«'"'•.          .          .          .  3  to     6 

Alumina          ..........  1                    ,, 

The  silica  content  of  a  natural  oxide  varies  very  much,  in  accordance  with  the 
district  from  which  it  is  taken.  Best  Dutch  material  seldom  contains  more  than 
4  to  5  per  cent.  Belgian  oxide  may  contain  from  10  to  12  per  cent.,  whilst  oxide 
occurring  in  this  country  has  been  known  to  contain  so  much  as  20  per  cent,  of 
silica  and  alumina.  The  proportion  of  silica  present  has  some  considerable  effect  on 
the  relative  density  of  the  various  oxides.  In  general  the  following  figures  may 
be  taken  as  representing  the  volume  equivalent  to  1  ton — 

Dutch  oxide      .          .          .          .          .          .          .          .          .  .  45  cubic  feet  per  ton. 

Belgian  oxide    .          .         .  .          .          .          .          .     40       „         „          „ 

Wiltshire  oxide  .          .          .          .          .          .  • .     35       „         „          ,, 

The  active  material  in  bog-ore  is  not  the  actual  oxide,  but  the  oxide  plus  a 
certain  amount  of  water  of  combination,  i.e.  a  hydrated  ferric  oxide,  Fe203,  H20.  In 
addition  to  this  moisture  the  material  as  used  should  contain  a  further  quantity  of 
water,  usually  from  20  to  30  per  cent.  For  effective  working  the  moisture  should 
never  be  less  than  the  lower  limit  given.  In  practice  it  is  generally  realized  that  the 
material  should  be  in  such  a  state  as  regards  moisture  that  it  will,  when  pressed  in  the 
hand,  bind  like  snow.  In  common  with  natural  oxides  the  artificial  varieties  are 
employed  with  a  similar  degree  of  moisture.  The  made-up  material  is  usually  more 
active  than  the  natural  product,  owing  to  a  rather  higher  content  of  ferric  hydrate 
(which  may  reach  so  much  as  70  to  75  per  cent.),  and  on  account  of  the  elimination  of 
vegetable  matter. 

When  foul  gas  containing  sulphuretted  hydrogen  is  passed  through  a  vessel 
filled  with  oxide  of  iron  the  sulphuretted  hydrogen  alone  is  extracted,  the  oxide 
having  no  affinity  for  carbon  disulphide  or  carbon  dioxide.  The  absorption  of  the 
sulphuretted  hydrogen  occurs  in  two  distinct  ways,  which  may  be  shown  as  follows — 

(1)  Fe203,  H20  +  3H2S  =  Fe2S3  +  4H20  (ferric  sulphide). 

(2)  Fe203,  H20  +  3H2S  =  2FeS  +  S  +  4H20  (ferrous  sulphide). 

It  will  be  noted  that  in  the  first  instance  ferric  sulphide  is  formed,  whilst  in  the 
alternative  equation  ferrous  sulphide  and  free  sulphur  result. 

After  a  time  the  material  ceases  to  absorb  sulphuretted  hydrogen,  but  can  be 
returned  to  a  state  of  activity  by  "the  process  known  as  "  revivification."  .  For  this 
purpose  it  is  removed  from  the  purifying  boxes,  spread  out  in  a  thin  layer,  turned 
over,  and  exposed  to  the  action  of  the  oxygen  in  the  atmosphere.  By  this  means  the 
iron  sulphides  are  oxidized  and  assume  their  original  character  with  the  deposition 
of  free  sulphur — 

(a)  2Fe2S3  +  30 8  +  2H20  =  2Fe203,H20  +  3S2. 
(6)  4FeS      +  302  +  2H20  =  2Fe203,H20  +  2S2. 

The  material,  together  with  the  free  sulphur,  is  then  returned  to  the  purifier, 
when  precisely  the  same  reactions  recur.  Revivification  may  then  be  carried  out 

c  c 


386  MODERN   GASWORKS   PRACTICE 

again,  and  the  oxide  repeatedly  returned  to  the  purifiers  until  it  contains  upwards  of 
55  or  60  per  cent,  of  sulphur,  beyond  which  figure  it  will  not  be  found  economical 
to  go. 

So  far  as  the  other  mediums  employed  for  the  removal  of  sulphuretted  hydrogen 
are  concerned,  Weldon  mud,  a  by-product  of  the  bleaching  industry,  owes  its  activity 
to  the  presence  of  manganese  dioxide.  The  reactions  occurring  are  very  similar  to 
those  appertaining  to  oxide  of  iron,  a  manganese  sulphide  capable  of  regeneration 
resulting.  In  many  respects  Weldon  mud  is  superior  to  oxide  of  iron  for  purification 
purposes.  It  cannot,  however,  be  obtained  now  owing  to  the  abandonment  of  the  old 
Weldon  chlorine  process.  The  chief  advantages  which  may  be  claimed  for  the 
material  are  increased  absorptive  activity  as  compared  with  oxide,  whilst  owing 
to  the  possibility  of  revivifying  it  in  situ  it  is  possible  to  work  up  the  spent  material 
to  a  high  sulphur  percentage  before  removing  it  from  the  purifier.  Owing  to 
its  sensitive  nature  Weldon  mud  was,  in  the  days  of  universal  lime  purification, 
particularly  suited  for  use  in  "  catch  boxes." 

Of  present-day  preparations  the  material  known  as  "  Lux  "  has  met  with  some 
considerable  success,  owing  to  the  sensitive  nature  of  its  operation.  "  Lux  "  is 
obtained  from  bauxite  (i.e.  ferric  aluminate),  which  is  powdered,  mixed  with  a  definite 
proportion  of  soda,  and  raised  to  a  red  heat.  This  results  in  the  formation  of  sodium 
aluminate  and  sodium  ferrate.  The  mass  consisting  of  these  two  sodium  compounds 
is  then  treated  with  water,  when  the  sodium  aluminate  dissolves  out  and  the  ferrate 
is  decomposed  and  forms  a  colloidal  hydrated  oxide. 

In  the  condition  as  delivered  for  use  "  Lux  "  contains  about  55  per  cent,  of  ferric 
oxide  and  20  per  cent,  of  alkaline  salts.  In  many  cases  it  is  desirable  to  mix  a  certain 
proportion  of  sawdust  with  the  material  as  it  is  received,  the  usual  ratio  being  3  parts 
of  "  Lux  "  to  1  part  of  sawdust.  It  is  said  by  some  that  with  "  Lux  "  the  absorp- 
tion of  SH2  takes  place  more  rapidly  than  with  bog-ore,  owing  to  the  fact  that 
the  ferric  hydrate  is  separated  out  in  a  finely  divided  state  during  the  manufacture 
of  the  material.  In  addition,  it  is  claimed  that  a  greater  percentage  of  sulphur 
may  be  obtained  before  the  material  is  finally  spent ;  but  some  trouble  may  be 
experienced  from  firing. 

Other  preparations  such  as  "  Ferrox  "  and  "  Brownox  "  contain  a  higher  pro- 
portion of  ferric  hydrate  than  is  the  case  with  the  natural  bog-ore.  This  accounts 
for  their  somewhat  vigorous  action,  although  in  their  preparation  the  addition  of 
other  ingredients  adds  to  their  efficiency.  Broadly  speaking  they  may  be  said  to 
result  from  burnt  spent  oxide,  which  is  obtained  from  sulphuric  acid  works, 
rendered  active  by  special  treatment.  This  treatment  varies  with  the  type  of 
material,  but  in  one  instance  it  consists  almost  solely  of  grinding  the  burnt  product 
in  a  disintegrator  with  the  addition  of  a  definite  proportion  of  soda  ash  and  saw- 
dust. A  product  known  as  Laming's  mass  was  at  one  time  a  great  favourite  in 
France,  Spain,  Italy  and  the  East.  This  consists  of  sawdust  mixed  with  lime  and 
wetted  with  a  solution  of  sulphate  of  iron. 

Purifying  material  in  this  country  is  generally  purchased  on  the  basis  of  analysis, 
i.e.  so  much  per  ton  for  a  certain  percentage  of  ferric  oxide.  The  spent  material  is 


387 

sold  in  accordance  with  its  sulphur  content,  i.e.  so  many  pence  for  each  unit  of  sul- 
phur. To  explain  this  it  may  be  assumed  that  a  spent  oxide  contains  50  per  cent, 
of  free  sulphur,  i.e.  50  units  per  ton.  If  the  price  per  unit  is  5d.,  the  value  of  the 
oxide  is  (50  X  5d.)—250d.  or  20s.  lOd.  per  ton.  Small  works  frequently  obtain  their 
oxide  on  a  loan  basis,  paying  (say)  a  penny  per  ton  of  coal  carbonized,  and  returning 
the  spent  material,  when  it  has  reached  a  certain  sulphur  content,  to  the  supplier. 
As  bog- ore  and  other  purifying  materials  are  frequently  bought  subject  to  certain 
conditions — particularly  with  regard  to  their  content  of  ferric  oxide  or  ferric 
hydrate — the  following  contract  form,  which  may  be  adopted  as  a  standard,  has 
been  included,  in  the  belief  that  it  may  prove  of  some  value  to  gas  engineers  having 
the  purchase  of  oxide  in  view. 

SPECIFICATION  AND  FORM  OF  TENDER  FOR  OXIDE  OF  IRON 

Description — The  tender  must  state  the  description  of  material  to  be  supplied. 

Quantity — The  quantity  of  material  required  is  ...  tons. 

Moisture — The  moisture  is  not  to  exceed  50  per  cent,  by  continued  heating 
at  212°  Fahr. 

Ferric  Oxide — The  quantity  of  ferric  oxide  (i.e.  Fe203,  inclusive  of  Fe203  as  FeO) 
is  to  be  not  less  than  25  per  cent,  in  the  material  (in  the  natural  state). 

Price— The  tender  is  to  be  at  a  rate  per  unit  of  ferric  oxide  (Fe203,  inclusive  of 
Fe203  as  FeO)  per  ton  in  the  condition  as  supplied. 

Delivery — (As  required). 

Notice  of  Arrival — A  week's  notice  of  probable  time  of  delivery  should  be  given 
by  seller  to  buyer. 

Analysis — Within  ten  days  of  each  delivery  the  seller  and  buyer  shall  exchange 
results  of  their  respective  analyses  of  sample.  Should  these  results  differ  in  the 
percentage  of  ferric  oxide  by  not  more  than  2  per  cent,  the  mean  shall  be  taken,  but 
if  the  difference  exceeds  2  per  cent,  then  a  remaining  sealed  portion  of  the  sample 
shall  be  submitted  to  an  independent  analyst  (nominated  by  the  buyer  and  agreed 
to  by  the  seller),  whose  decision  shall  be  final.  The  cost  of  such  analysis  shall  be 
borne  by  the  party  whose  result  is  the  more  divergent. 

Forfeiture — Should  the  analysis  of  the  sample  of  any  delivery  show  that  the 
conditions  herein  specified  are  not  complied  with,  then  it  shall  be  at  the  option  of 
the  buyer  to  make  such  deductions  from  the  account  as  shall  compensate  him  for 
loss  arising  from  the  non-compliance. 

Failure  of  Delivery — In  the  event  of  any  failure  on  the  part  of  the  seller  to  deliver 
the  material  of  stipulated  quality  and  otherwise  in  accordance  herewith,  the  buyer 
may  procure  a  corresponding  quantity  of  material  from  other  parties,  and  any  loss  i 
incurred  by  the  buyer  in  so  doing  is  to  be  borne  by  the  seller,  and  to  be  deducted  from 
any  sum  due  to  him,  or,  in  the  event  of  no  such  sum  being  due,  is  to  be  recoverable 
by  action  as  if  on  a  simple  contract  debt. 

Payment — Payment  shall  be  made  within  fourteen  days  of  agreement  as  to 
analysis,  less  2-J-  per  cent. 

Arbitration — Any  dispute  arising  out  of  or  in  connexion  with  this  contract  is 


388 


MODERN   GASWORKS   PRACTICE 


to  be  settled  by  arbitration  by  two  arbitrators  (one  to  be  named  by  each  party)  and 
an  umpire,  in  manner  provided  by  the  Arbitration  Act  of  1889  or  any  statutory 
modification  thereof. 

THE   EFFECTIVE   WORKING   OF   PURIFIERS 

It  is  seldom  advisable  to  put  bog- ore  into  operation  in  the  state  in  which  it 
arrives,  for  some  difficulty  may  be  experienced  in  getting  the  material  to  commence 
working  When  trouble  is  experienced  in  this  way,  the  admixture  of  a  small 
proportion  of  material  which  has  previously  been  in  use  will  generally  overcome 
the  difficulty. 


FIG.  257. — ROTATION  SYSTEM  OF  PURIFICATION. 


Present-day  systems  of  purification  may  be  classified  under  two  headings, 
namely — 

(a)  Series  purification.  (6)  Rotation  purification. 


1 


I 


f 

[ 


389 


390 


MODERN   GASWORKS   PRACTICE 


The  difference  between  the  two  systems  is  in  reality  a  constructional  one,  and 
depends  merely  upon  whether  a  set  of  purifiers  is  arranged  around  a  centre  valve, 
as  shown  in  Fig.  257,  or  in  a  line,  with  a  number  of  single  valves,  as  seen  in  Fig.  259. 
For  the  operation  of  the  rotation  system  it  is  not  necessary  that  the  four  purifiers 
should  be  set  one  at  each  corner  of  a  square,  although  this  arrangement  is  the  most 
convenient.  With  oxide  purification  the  modus- operandi  usually  adopted  is  that  of 
having  three  of  the  four  boxes  in  action  at  a  time  ;  that  is,  gas  is  passing  first  through 
the  first  box  or  "  taker,"  then  through  the  second,  and  lastly  through  the  third,  by 
which  time  it  is  wholly  deprived  of  sulphuretted  hydrogen.  After  a  time  the  oxide 
in  the  first  box  becomes  "  fouled  "  and  useless  for  the  further  extraction  of  SH2 
until  the  material  is  revivified.  No.  4  box  is  then  put  into  action  and  No.  1  box 
is  shut  off,  so  that  the  original  second  box  now  becomes  first  "  taker."  In  the 
meantime  No.  1  box  is  thrown  out,  revivified  and  remade,  and  is  then  ready  for 
action  once  more  as  the  final  box  when  required.  Thus  we  get — 

First  series  ->  1  ->  2  ->  3,  4  off. 

Second     „    ->  2  ->  3  ->  4,  1  off. 

Third      „    ->  3  ->  4  ->  1,  2  off. 

Fourth     „    ->  4  ->  1  ->  2,  3  off. 

In  this  way  each  purifier  comes  in  for  an  "  off  "  period,  so  that  it  may  be  dealt  with 
when  it  has  become  "  fouled."  The  system  of  working  as  described  applies  to  purifiers 
arranged  either  in  series  or  around  a  centre  valve.  It  should  be  mentioned  that  in 
the  majority  of  works,  with  the  exception  of  those  of  small  dimensions,  a  further 


FIG.  260. — ROTATION  SYSTEM  WITH  CATCH-BOXES. 

safeguard  against  the  possibility  of  sulphuretted  hydrogen  getting  through  to  the 
district  mains  is  provided  for  by  the  insertion  of  two  "  catch-boxes,"  as  shown  in 
%.  260. 

Within  recent  years  a  new  and  effective  method  of  arranging  the  series  of  purifiers 
has  come  into  operation,  and  is  known  as  "  backward  rotation."  It  differs  essen- 
tially from  the  ordinary  system  in  that  when  a  box  operating  first  in  the  series 
becomes  fouled  the  clean  box  is  placed  first  in  position  instead  of  last.  Thus  if 
four  purifiers  are  operating  in  series,  we  shall  have — 

First  series  ->l->2->3^4  * 

Second     ,,    ->4->1^2->3 

Third  .->  3  ->  4  ->  1  ->  2,  and  so  on. 


THE   DRY   PURIFICATION   OF   COAL   GAS          391 

By  the  adoption  of  this  method  it  is  claimed  that  where  "  catch-boxes  "  have 
previously  been  in  use  they  may  be  dispensed  •  with,  although  such  a  procedure 
would  seem  to  be  attended  by  some  risk.  The  author  finds  that  where  a  works 
has  outgrown  its  purifying  capacity  the  method  is  particularly  suitable,  and 
instances  are  known  where  the  cubical  capacity  available  is  so  low  as  0'25 
cubic  feet  per  1,000  cubic  feet  of  gas  per  diem,  and  yet  no  trouble  is  experienced. 

Another  method  which  has  found  some  favour  is  that  known  as  "  forward 
rotation."  That  is  to  say,  when  the  first  "  taker  "  becomes  fouled  it  is  placed  at 
the  end  of  the  series,  thus — 

First  series  ^lH^2^3->4 
Second     „    ->2^-3-^4->l,  etc. 

When  working  in  this  manner  it  would  seem  essential  that  "  catch-boxes  " 
should  be  used,  owing  to  the  tendency  of  the  final  purifier  to  throw  off  a  certain 
amount  of  sulphuretted  hydrogen.  In  fact  it  may  be  said  that  in  all  cases  the 
introduction  of  "  catch-boxes,"  although  theoretically  unnecessary,  is  a  wise 
precaution  against  sudden  eventualities. 

THE   ADMISSION  OF  AIR 

Oxide  of  iron  is  generally  used  in  the  purifiers  in  layers  varying  from  8  inches 
to  10  inches  in  depth,  although  in  some  cases  it  is  still  customary  to  adhere  to  deeper 
tiers  of  about  30  inches.  The  last-named,  however,  frequently  give  rise  to  excessive 
back  pressure,  and  are  not  to  be  advised  in  the  ordinary  way.  A  space  of  not  less 
than  2  inches  should  always  be  allowed  between  the  top  surface  of  one  layer  and 
the  underneath  surface  of  the  grid  above  it.  Oxide  as  it  becomes  fouled  increases 
in  bulk — hence  this  precaution. 

Partial  revivification  in  situ  is  almost  always  arranged  for  nowadays,  the  small 
quantity  of  air  admitted  during  the  process  considerably  adding  to  the  working 
life  of  the  material.  Care  has,  of  course,  to  be  exercised  with  regard  to  the  quantity 
of  air  introduced.  The  usual  allowance  is  2|  per  cent,  for  every  1  per  cent,  of 
sulphuretted  hydrogen  present,  and  astheSH2  amounts  in  normal  cases  to  about 
i  per  cent.,  the  theoretical  quantity  of  air  required  is  about  1  per  cent.  Some  engineers 
arrange  for  15  cubic  feet  of  air  per  1,000  cubic  feet  of  gas.  The  admission  of  air 
may  be  arranged  for  in  two  ways.  It  may  be  sucked  in  from  the  atmosphere  through 
a  pipe  on  the  inlet  or  vacuum  side  of  the  exhauster  (in  which  case  the  air  should  be 
drawn  through  a  meter  so  that  its  volume  may  be  measured),  or  it  may  be  injected 
direct  into  the  mains  leading  to  the  purifiers  by  means  of  an  ordinary  steam  injector. 
An  effective  means  of  arranging  an  injector  system 'is  shown  in  Fig.  261.  On  the 
larger  works  an  injector  may  be  fitted  to  the  inlet  of  each  purifier,  whilst  in  small 
works  a  run  of  two  or  three  hours'  duration  every  day  should  answer  the  purpose. 
When  air  is  sucked  through  from  the  inlet  side  of  the  exhauster  it  is  advisable  to 
introduce  some  safeguard  in  case  sudden  pressure  might  arise  from  any  cause.  The 
safety  seal  shown  in  Fig.  262  is  simple  and  convenient.  It  consists  of  a  cast-iron 
box  about  12  inches  square  by  4  inches  deep,  with  a  flat  cover  securely  jointed. 
Water  should  be  poured  in  at  B  until  it  overflows  from  the  bib-cock  C.  The  outlet 


392 


MODERN   GASWORKS   PRACTICE 


Injectcr 


Inlet 

-Gas     — 1- 
Maln 


4            Cock  for  Regulation 
of  Steam  Supply 

Air  Inlet 

Inlet  Pipe 
Rfrom  Injector 
1 

1  m 

c 

,    / 

To  Purifier 


Steam  Inlet 


FIG.  261. — AIR  INJECTOR  FOR  DRY  PURIFIERS,  SHOWING  METHOD  OF  CONNECTING  UP. 

of  the  meter  is  connected  to  A,  and  the  service  D  leads  to  the  gas  main.  The  base 
of  the  seal-pipe  A,  which  is  screwed,  is  so  adjusted  that  it  dips  below  the  surface  of 
the  water  to  the  depth  of  about  an  inch.  In  the  event  of  back-pressure  the  water 

will  be  depressed  and  rise  in  the  pipe 
A,  which  should  not  be  less  than  24 
inches  to  30  inches  in  height. 

It  should  be  borne  in  mind  that 
most  coal  gas  will  contain  a  certain 
amount  of  oxygen,  and  the  quantity 
varies  to  some  considerable  extent.  It 
is  important,  therefore,  to  test  the 
gas  for  oxygen-  before  blindly  admit- 
ting air,  otherwise  the  recognized  limit 
may  be  considerably  exceeded.  In  ex- 
ceptional cases  the  gas  itself  contains  sufficient  oxygen  without  the  introduction  of 
a  further  quantity  from  the  atmosphere.  It  is  interesting  to  note  here  the  remarks 
of  one  authority  who,  as  a  result  of  a  great  number  of  experiments,  found  that  an 
amount  of  oxygen  in  excess  of  0'3  per  cent,  was  never  absorbed  from  the  gas  in  the 
purifiers.  In  view  of  this,  it  is  contended  that  as  from  0-2  to  04  per  cent,  of 
oxygen  is  almost  sure  to  gain  admittance  during  the  period  for  which  the  retort 
doors  are  open,  there  is  no  necessity  to  add  a  further  amount  to  the  purifiers. 

When  air  is  admitted  at  some  point  prior  to  the  purifiers  it  must  not  be  over- 
looked that  there  is  always  the  possibility  of  its  encouraging  undesirable  reactions 
in  the  wet  purification  plant.  It  is,  however,  an  excellent  plan  to  arrange  for  the 
air  to  be  introduced  on  the  inlet  of  the  clean  water  scrubber. 

The  merits  of  the  "  backward  rotation  "  system  are  chiefly  dependent  upon  the 
part  played  by  the  admitted  air.  For  some  time  it  has  been  generally  understood 
that  the  material  in  a  purifier  cannot  simultaneously  extract  sulphuretted  hydrogen 


IFio.  262. — SAFETY  SEAL  FOR  AIR  ADMISSION. 


THE  DRY   PURIFICATION   OF   COAL   GAS          393 

from  the  gas  and  undergo  revivification.  The  assumption  is  not  entirely  accurate, 
as  the  process  of  sulphiding  invariably  takes  place  at  a  very  much  more  rapid  rate 
than  does  the  absorption  of  air.  In  the  case  of  "  backward  rotation,"  therefore,  a 
purifier  gradually  passes  from  the  position  of  first  "  taker,"  where  sulphiding  alone 
occurs,  to  the  end  of  the  series  where  the  oxygen  is  permitted  to  carry  out  revivi- 
fication undisturbed.  In  this  way  each  purifier  is  accorded  a  period  of  rest  in  which 
to  prepare  for  taking  its  place  once  more  at  the  head  of  the  series.  Accordingly, 
with  alternate  periods  of  sulphiding  and  revivification,  the  boxes  may  be  operated 
for  a  lengthened  time  before  requiring  remaking,  and  the  material  may  be  worked 
up  to  a  higher  sulphur  content.  In  all  it  will  only  be  necessary  to  make  from  three 
to  four  changes  before  the  material  is  finally  spent  (containing  about  55  per  cent,  of 
free  sulphur),  which  contrasts  very  favourably  with  the  old  method,  of  which  Lewis 
T.  Wright  wrote  in  1895,  "  Oxide  can  be  economically  sulphided  and  oxidized  sixteen 
times,"  this  meaning  that  before  the  material  was  economically  spent  it  could  be 
thrown  in  and  out  of  the  purifier  sixteen  times. 

For  most  efficient  results,  so  far  as  revivification  in  situ  is  concerned,  a  slight 
excess  of  air  above  the  theoretical  quantity  indicated  by  the  amount  of  sulphuretted 
hydrogen  present  should  be  employed.  Furthermore,  the  capacity  of  the  plant 
should  be  ample,  otherwise  the  air  will  not  produce  its  due  effect. 

THE   EFFECT   OF   ADDING  AIR 

When  revivification,  owing  to  admitted  air,  is  taking  place  in  a  purifier,  a  rise  in 
temperature,  usually  amounting  to  about  5°Fahr.,  will  be  noticed  between  the  inlet 
and  outlet.  It  is  unnecessary  to  add  that  no  little  precaution  is  necessary  in  the 
regulation  of  the  quantity  of  air  used,  chiefly  owing  to  its  diluent  effect  as  regards 
the  final  illuminating  and  calorific  power  of  the  gas,  and  also  with  regard  to  cur- 
tailing any  abnormal  rise  in  temperature.  It  is  necessary  to  bear  in  mind  that 
should  any  excessive  local  heating  of  the  oxide  take  place,  instead  of  a  sulphide  or 
a  normal  sesquisulphide  being  obtained,  a  disulphide  of  iron  is  formed,  or  even  a 
sulphate.  This  is  due  to  too  vigorous  oxidation.  In  the  case  of  the  disulphide  or 
sulphate  of  iron,  revivification  is  impossible,  and  a  portion  of  the  material  loses  its 
activity  in  consequence.  There  is,  however,  a  remedy,  for  if  an  alkali  is  added  it 
will,  on  account  of  its  basic  properties,  release  the  iron  from  its  undesirable  com- 
bination with  the  sulphur.  The  alkali  may  be  added  in  the  form  of  ammonia  from 
the  scrubber,  which  may  be  by-passed  for  a  short  period  ;  but  preferably  a  small 
proportion  of  powdered  slaked  lime  should  be  admixed  to  the  oxide  when  it  is 
removed  from  the  box. 

So  far  as  the  diluent  properties  of  air  are  concerned,  mention  may  first  be  made 
of  the  oft- quoted  work  of  Audouin  and  Berard,  carried  out  in  1862.  These  investi- 
gators found  that — 

1  per  cent,  of  air  reduces  illuminating  power  by     6  per  cent. 

2  „  „  „  „  „       „    11 

3  „  „          „  „  „       „    18 

4  „  „          „  „  „       „    26 

and  if  45  per  cent,  of  air  is  added  the  loss  of  candle-power  amounts  to  ICO  per  cent. 


394  MODERN   GASWORKS   PRACTICE 

Later  results  have  been  given  by  Wurtz,  who  states  that — 

3  per  cent,   of  air  causes  15-69  par  cant,  loss  in  light. 
5         „  „  „          24-0 

The    most   recent   experiments   in    this    direction   have    been    carried  out  by 
Dr.  W.  B.  Davidson.     The  figures  he  gives  are  the  following — 

1  per  cent,  of  oxygen  added  decreases  candle-power  by  3  per  cent,  and  calorific  power  by 

1  per  csnt. 
1  per  cent,  of  nitrogen  added  decreas3s  cindle-power  by  2'6  per  C3nt.  and  calorific  power 

by  1  per  cent. 

So  far  as  carbon  dioxide  is  concerned,  Davidson  states  that  1  per  cent,  added  to  an 
average  sample  of  coal  gas  will  reduce  the  illuminating  power  by  3J  per  cent. 

REVERSE  ACTION 

In  the  ordinary  way,  the  gas  enters  at  the  base  of  the  purifiers  and  passes  upwards 
through  the  material.  Recently,  however,  it  has  been  pointed  out  that  reverse  flow 
(i.e.  gas  entering  above  the  material  and  passing  downwards)  possesses  a  number  of 
advantages,  so  that  the  system  is  growing  in  popularity.  Foremost,  perhaps,  is  the 
back-pressure  consideration  ;  and  when  a  purifier  gives  trouble  in  this  direction  an 
effectual  remedy  will  be  found  in  the  reverse  flow.  This  is  largely  on  account  of  the 
increased  area  of  oxide  exposed  to  the  gas,  which  (owing  to  the  grids)  is  nearly  halved 
when  the  flow  is  in  the  usual  upward  direction.  When  excessive  pressure  is  thrown 
by  a  box,  it  is  usually  attributable  to  the  first  (i.e.  the  bottom)  tier,  whilst  a  common 
remedy  is  to  draw  a  slide,  and  so  by-pass  the  one  layer.  In  this  respect  the  down- 
ward travel  certainly  makes  matters  easier,  for  the  lid  may  be  lifted  and  the  top 
material  lightened  (or  exchanged  for  new)  with  little  delay.  Thus  the  efficiency  of 
the  box  is  increased  and  not  reduced  materially,  as  is  the  case  when  a  layer  is  slipped. 

It  occasionally  happens  that  a  purifier  suffers  as  regards  activity  owing  to  the 
material  becoming  too  dry.  The  reverse  system  in  such  cases  will  usually  provide 
a  remedy  ;  and  if  the  box  is  made  first  "  taker,"  the  saturated  gas  coming  away  from 
the  scrubbing  plant  will  deposit  its  moisture  on  the  material  and  the  purifier  cover, 
this  in  time  percolating  through  the  layers,  with  the  desired  results.  On  the  other 
hand,  when  gas  is  admitted  to  the  bottom  of  the  vessel,  the  water  is  merely 
deposited  in  the  box,  and  runs  away  through  the  seals.  The  top  tier  of  oxide  in 
a  downward-current  purifier  is  frequently  found  to  be  in  a  muddy  condition  for  a 
depths  of  two  or  three  inches  when  the  box  is  working  as  first  "  taker." 

A  small  point  worthy  of  notice  is  that  of  revivification.  When  air  is  admitted 
to  a  box,  it  is  the  material  at  the  bottom  which  (under  the  common  system)  derives 
the  greatest  benefit  from  this,  and  is,  consequently,  revivified  to  a  somewhat  greater 
extent  than  the  upper  tiers.  If  alternate  flow  is  provided  for,  however,  the 
uppermost  layers  are  able  to  derive  full  benefit  from  the  oxygen  present. 

Reversal  of  current  is,  of  course,  not  to  be  recommended  in  the  case  of  oil  gas 
purification. 

Purifiers  which  are  fitted  for  the  travel  of  gas  in  the  usual  upward  direction  may 
readily  be  modified  so  as  to  cause  the  gas  to  take  a  downward  path.  Providing  that 


THE   DRY   PURIFICATION    OF   COAL   GAS          395 

alternating  up  and  down  travel  is  not  desired,  the  easiest  means  is  that  of  merely 
transposing  the  long  outlet  pipe,  which  exterfds  above  the  grids  in  the  box  to  the  inlet 
main.  Special  valves,  such  as  Milbourne's  (Fig.  263),  can  now  be  had  for  reversing 
the  direction  of  flow  at  will,  whilst  Dempster's  patent  device,  which  is  self- 
explanatory,  is  shown  in  Fig.  264. 


FIG.  263. — MILBOURNE'S  VALVE  FOR  UP  OB  DOWN  FLOW. 

At  the  present  day  it  is  common  to  find  a  supply  of  live  steam  arranged  for  in 
the  oxide  purifiers.  Some  precaution  is  necessary  in  the  use  of  steam  in  this  way,  as 
excessive  moisture  may  give  rise  to  abnormal  back-pressure,  resulting  in  the  shutting- 
down  of  the  box.  The  chief  advantage  of  the  steam  is  the  fact  that  it  accounts  for 
some  rise  in  temperature  of  the  gas,  whereby  the  oxide  is  maintained  in  a  warm  con- 
dition, which  is  conducive  to  its  effective  working.  For  this  reason  it  is  found  that 


396 


MODERN   GASWORKS   PRACTICE 


the  efficiency  of  a  purifier  may  be  enhanced  by  arranging  for  a  steam  coil  in  the  gas 
inlet  or  in  the  base  of  the  box — no  live  steam  coming  actually  in  contact  with  the 
gas.  Raising  the  temperature  of  the  inlet  gas  by  10°  to  20°  Fahr.  will  frequently  be 
found  to  get  over  any  difficulty  arising  from  sluggish  material.  In  this  respect 
it  will  be  noticed  that  when  purifiers  are  partly  buried  the  average  temperature  of 
the  gas  will  be  somewhat  higher  than  when  the  vessels  are  above  ground  in 

open    sheds  or    exposed    to    the 
weather. 

When  oxide  is  discharged 
from  a  purifier,  after  the  prelimin- 
ary foulings,  it  should  not  be  re- 
turned to  the  box  before  all 
lumps  are  broken  and  the  whole 
reduced  to  a  powdery  nature. 
Thorough  pulverization  will  in- 
crease the  efficiency  of  an  oxide 
very  considerably.  Experiments 
have  shown  that  whilst  one 
sample  of  unpowdered  oxide  after 
four  absorptions  contained  37-3 
per  cent,  of  sulphur,  the  same 
material  in  the  pulverized  state 
contained  47-1  per  cent.,  or  an 
increase  in  sulphur  of  27  per  cent. 
The  chief  difficulty  is  that  of  en- 
suring that  the  smaller  lumps, 
about  half  an  inch  in  diameter, 
shall  be  effectively  powdered. 
With  hand  labour  afone  the  task 
is  most  laborious,  and  the  only 
satisfactory  result  is  obtained 
with  one  of  the  many  special  dis- 
integrators now  to  be  had. 

Oxide  may  be  prevented 
from  caking  heavily  in  the  puri- 
fiers by  adding  a  small  propor- 
tion of  coarse  sawdust  on  each  occasion  that  the  material  is  changed ;  whilst 
it  should  also  be  maintained  in  an  alkaline  condition.  Even  though  ammonia 
be  allowed  to  travel  forward  from  the  scrubber,  the  oxide  may  be  found  to  give 
an  acid  reaction  ;  and,  whether  acid  or  neutral,  enough  finely  powdered  slaked 
lime  should  be  added  to  the  material  to  make  it  alkaline  before  it  is  returned  to 
the  purifier.  The  formation  of  prussian  blue,  and  the  general  effect  of  cyanide 
•compounds  on  the  purifying  material  is  fully  discussed  in  the  previous  chapter 
.(page  369). 


FIG.  264. — DEMPSTER'S  REVERSING  VALVE-BOX. 


THE   DRY   PURIFICATION   OF   COAL   GAS          397 

MEETING   EMERGENCIES 

Whatever  care  may  be  bestowed  upon  the  purification  plant,  it  is  occasionally 
the  experience  of  every  engineer  to  find  that  a  perceptible  trace  of  sulphuretted  hydro- 
gen is  getting  through  into  the  finished  gas.  When  such  is  the  case,  quick  action 
is  usually  necessary,  and  the  following  three  remedies  are  suggested — 

(1)  If  a  small  proportion  of  air  is  injected  into  the  gas  at  the  outlet  of  the  purifiers, 
the  trace  will  very  frequently  be  temporarily  cleared. 

(2)  If  the  material  in  the  purifiers  is  obviously  at  fault,  the  top  tier  of  the  final 
box  may  be  rendered  extremely  active  by  being  covered  with  a  2-inch  layer  composed 
of  fresh  oxide  and  hydrated  oxide  (i.e.  chemically  prepared  material).     The  last 
named  is  prepared  by  mixing  together  about  1  ton  of  ground  copperas  with  an  equal 
amount  of  lime,  care  being  taken  to  ensure  that  the  lime  is  present  in  sufficient 
quantity  to  make  the  mixture  alkaline. 

(3)  The  trace  of  sulphuretted  hydrogen  may  be  due  to  chemical  action  in  the 
gasholder.     The  cause  of  and  remedy  for  such  derangements  are  discussed  in  the 
next  chapter. 

LIME   PURIFICATION 

Lime  in  the  hydrated  or  slaked  condition  is  an  active  absorbent  for  sulphuretted 
hydrogen  and  carbon  dioxide,  and — under  certain  conditions — is  capable  of  removing 
a  proportion  of  the  remaining  sulphur  compounds.  On  the  smallest  of  works,  where 
the  amount  of  sulphur  recoverable  would  (owing  to  cost  of  carriage  and  other  con- 
siderations) not  materially  affect  the  receipts,  lime  is  used  exclusively.  On  the  larger 
works  its  use  has  been  largely  discontinued,  owing  to  there  no  longer  being  any 
statutory  objection  to  the  small  quantity  of  sulphur  compounds — other  than 
sulphuretted  hydrogen — travelling  forward  to  the  district.  The  admixture  with  coal 
gas  of  water  gas,  which  contains  but  a  small  proportion  of  sulphur  compounds,  has 
tended  to  curtail  considerably  the  total  quantity  of  these  compounds  in  the  mixed 
gases.  In  the  case  of  those  concerns  where  coal  gas  alone  is  manufactured,  the  re- 
moval of  a  portion  of  the  carbon  disulphide  is  still  usual.  In  some  instances  it  is 
effected  by  methods  known  as  "  hot  "  purification,  but  more  generally  with  the  aid 
of  lime. 

The  sulphur  compounds  remaining  in  the  gas  after  the  sulphuretted  hydrogen 
has  been  removed  consist  almost  wholly  of  carbon  disulphide  (which  is  present  to  the 
extent  of  about  0-02  per  cent.).  Of  the  remainder,  thiophene  is  the  chief  constituent, 
but  so  far  the  other  compounds  have  not  been  distinguished. 

In  studying  purification  by  lime  it  is,  primarily,  necessary  to  bear  in  mind  that 
of  the  three  acid  gases  involved,  carbon  dioxide  has  the  strongest  acidic  properties, 
sulphuretted  hydrogen  following  next,  with  carbon  disulphide  last  in  order.  Thus 
when  the  crude  gas  meets  an  active  base  such  as  slaked  lime  there  is  a  tendency  for 
the  most  vigorous  acid  to  be  absorbed  first.  The  combination  between  lime  and 
CO  2  takes  place  on  simple  lines,  as  follows — 

Ca(OH)2  +  CO  2  =  CaC03  +  H20. 


398  MODERN   GASWORKS   PRACTICE 

Sulphuretted  hydrogen  reacts  with  lime  in  the  following  manner — 
Ca(OH)2  +  SH2  -  CaS  +  2H20. 

Thus,  as  before  explained,  the  whole  of  the  purification  can,  by  employing  a  suffi- 
ciency of  material,  be  carried  out  with  lime.  The  great  drawback  to  such  methods, 
however,  is  the  loss  of  the  sulphur,  which  cannot  be  recovered  in  useful  form,  as  is 
the  case  where  oxide  of  iron  is  employed.  As  explained  above,  when  the  gas  from 
the  wet  purification  plant  enters  the  first  (lime)  purifier,  the  C02  is  absorbed  to  the 
greatest  extent,  although  some  sulphuretted  hydrogen  is  also  removed.  As  the  process 
proceeds,  this  sulphuretted  hydrogen  is  displaced  by  the  stronger  acidic  nature  of 
the  CO  2,  and  the  spent  material  consists  almost  wholly  of  the  carbonate.  The 
manner  in  which  the  sulphide  is  displaced  is  shown  as  follows : — 

CaS  +  C02  +  H20  =  CaC03  +  SH2. 

If  a  small  proportion  of  air  is  admitted  to  the  purifier,  a  certain  amount  of  the  calcium 
sulphide  will  be  converted  into  free  sulphur,  and  will  thus  escape  ultimate  decom- 
position by  C02. 

In  preparing  ordinary  dry  lime  for  use  in  purifiers,  the  material  should  be  well 
slaked  with  water,  and  as  much  as  possible  of  the  "  core  "  (i.e.  inert  matter,  such  as 
chalk,  stones,  etc.)  should  be  removed  by  screening.  In  addition  to  the  water 
actually  required  for  slaking,  the  lime  should  contain  a  further  30  per  cent,  of 
moisture.  Excessive  watering  will,  however,  give  rise  to  caking.  Caking,  and  con- 
sequent loss  in  power  of  absorption,  may  also  result  from  too  much  sulphuretted 
hydrogen  having  been  passed  through  the  lime,  this  occasionally  occurring  in  those 
boxes  which  are  set  aside  for  the  removal  of  CS2.  So  far  as  the  thickness  of  the 
layers  of  lime  is  concerned,  it  may  be  pointed  out  that  a  depth  of  about  8  inches 
is  preferable  to  the  thinner  layers  of  4  and  5  inches  which  were  often  employed  in 
the  past.  Whatever  the  type  of  purifying  material,  a  thin  layer  is  likely  to  "  blow  " 
and  thus  permit  a  certain  amount  of  gas  to  escape  untreated. 

When  gas  manufactured  at  the  larger  works  is  to  be  freed  from  the  whole  of 
its  impurities,  it  is  usual  to  instal  a  system  in  which  oxide  of  iron  and  lime  are  used 
in  conjunction.  In  this  way  the  greater  proportion  of  the  sulphuretted  hydrogen 
may  be  recovered  and  not  wasted.  Many  methods  of  operating  the  purifiers  for  this 
purpose  have  been  employed,  but  the  whole  principle  may  be  readily  grasped  by  a 
consideration  of  the  well-known  Beckton  system.  It  consists  in  the  main  of  four 
sets  of  purifiers  operated  in  rotation — 

First  set.         Contains  lime.      These  remove  the  whole  of  the  CO2  and  some  SH2,  which  is  after- 
wards displaced  by  C02.     Some  CS2  is  also  absorbed. 
Second  set.     Contains  oxide     These  remove  the  whole  of  the  SH2,  including  any  which  may 

of  iron.  be  displaced  from  the  lime  in  the  previous  set. 

Third  set.        Contains  lime.     This  lime  has  been  previously  "  sulphided  "  and  removes  the 

bulk  of  the  CS2.     It  will  not  remove  the  whole  of  this  impurity. 

Fourth  set.     Contains  oxide     These  vessels  act  as  "  catch-boxes  "  and  remove  any  SH2  which 
of  iron.  is  disengaged  from  the  third  set. 

In  order  to  understand  the  method  of  working,  it  must  be  borne  in  rnind  that 
ordinary  slaked  lime — per  se — has  no  action  upon  carbon  disulphide.  The  chemical 


THE   DRY   PURIFICATION   OF   COAL    GAS          399 

reactions  involved  in  the  elimination  of  this  impurity  are  somewhat  complex  and  are 
set  out  below.  First,  it  will  be  seen  that  the  calcium  hydrate  must  be  "  sulphided  " 
by  passing  through  it  a  stream  of  sulphuretted  hydrogen.  For  this  purpose  the 
crude  gas,  after  travelling  through  the  first  set  of  purifiers,  is  led  direct  into  the  third 
set,  the  oxide  vessels  comprising  the  second  series  being  by-passed  for  the  time. 
Working  in  this  way  is  continued  until  sulphuretted  hydrogen  is  noticed  at  the  outlet 
of  the  lime  boxes  forming  the  third  set.  At  this  juncture  the  two  oxide  vessels 
(second  set)  are  put  into  action.  The  lime  vessels  forming  the  third  set  are  then 
in  a  condition  to  absorb  carbon  disulphide,  and  purification  proceeds  as  outlined 
above.  Of  the  total  CS2  present,  up  to  20  per  cent,  may  be  removed  by  the  first 
lime  vessels,  55  per  cent,  by  the  sulphided  boxes,  whilst,  about  25  per  cent,  will 
remain  in  the  gas. 

The  total  amount  of  sulphur  compounds  (other  than  SH2)  in  crude  coal  gas 
varies  in  normal  cases  from  35  to  50  grains  per  ICO  cubic  feet,  although  in  exceptional 
instances  the  figure  may  rise  to  60  grains. 

CHEMICAL   REACTIONS   IN  CS2   REMOVAL 

The  exact  nature  of  the  chemical  reactions  occurring  during  the  removal  of  carbon 
disulphide  is  still  open  to  question.  It  should  be  stated  at  once,  however,  that 
although  the  active  medium  consists  primarily  of  calcium  sulphide,  and  although 
this  compound  in  the  moist  state  is  capable  of  absorbing  CS2,  the  reaction  is 
certainly  not  represented  by  the  following  simple  equation — 

CaS  +  CS2  =  CaCS3. 

The  most  enlightening  work  on  the  subject  has  been  carried  out  by  Veley  (1885), 
whose  theory  is  generally  accepted  as  correct.  This  investigator  concluded  that  the 
compound  which  absorbs  the  CS2  is  not  calcium  hydrosulphide  (as  has  sometimes 
been  supposed),  but  calcium  hydroxyhydrosulphide  (CaS,H20,  or  CaOH.SH). 
The  hydroxyhydrosulphide,  it  is  understood,  is  formed  in  the  following  manner — 

(1)  Calcium  hydrosulphide  results  in  the  first  place — 

Ca(OH)2  +  2H2S  =  Ca(SH)2  +  2H20. 

This  compound  Ca(SH)2  has  no  action  on  the  CS2. 

(2)  By  the  addition  of  water  or  oxygen  the  hydrosulphide  is  then  converted 

into  the  hydroxyhydrosulphide — 

(a)  Ca(SH)2  +  H20  -  CaOH,SH  +  SH2 

or 
(6)  2Ca(SH)2  +  02  =  2CaOH,SH  +  28. 

The  former  reaction  is  the  one  most  likely  to  occur  in  practice,  for  oxygen 
will  seldom  be  present  at  this  stage. 

(3)  The  CS2  and  calcium  hydroxyhydrosulphide  interact  as  follows — 

(a)  2CaOH,SH  +  CS2  =  SH2  +  Ca(OH)2,CaCS3 

or 
(6)  3CaOH,SH  +  CS2  +  H20  =  2SH2  +  2Ca(OH)2,CaCS3. 


400  MODERN   GASWORKS   PRACTICE 

In  either  case  it  will  be  seen  that  sulphuretted  hydrogen  is  thrown  off  and  is  absorbed 
in  the  final  oxide  boxes. 

Derangements  with  lime  purification  are  only  too  common,  owing  to  the  difficulty 
of  applying  in  practice  a  series  of  somewhat  delicate  chemical  operations.  Occasion- 
ally the  sulphided  boxes  will  actually  throw  off  carbon  disulphide,  and  thus  increase 
instead  of  reduce  the  sulphur  compounds  in  the  gas.  If  adequate  precautions  are 
taken,  however,  this  trouble  should  not  occur.  The  chief  necessity  is  that  of 
ensuring  that  no  C02  should  be  allowed  to  travel  forward  to  the  CS2  boxes.  The 
CO  2  will  instantly  displace  the  carbon  disulphide,  which  must  then  travel  forward 
with  the  gap.  An  important  point  to  bear  in  mind  is  that  the  sulphiding  action 
should  never  be  carried,  out  at  a  low  temperature,  otherwise  the  activity  of  the 
material  may  be  impaired.  The  temperature  of  the  lime  during  this  operation  should, 
if  possible,  be  maintained  at  about  50°  Fahr.,  although  this  will  not  always  be  possible 
during  winter.  An  inactive  purifier  may  frequently  be  revivified  by  the  injection  of  a 
small  quantity  of  air,  the  oxygen  probably  reacting  with  the  hydrosulphide  and 
oxidizing  it  to  hydroxyhydrosulphide,  as  shown  in  the  above  equation. 

THE   CONSTRUCTION   OF   PURIFIERS 

Purifiers,  as  used  in  gasworks,  are  generally  constructed  of  cast  iron  (ferro- 
concrete has  lately  been  experimented  with),  and  may  be  classified  into  three  distinct 
groups — 

(a)  Water-lute  vessels,  the  type  originally  employed  and  still  largely  made  use 
of,  the  lute  varying  from  15  inches  to  40  inches  deep. 

(6)  Dry-lute  purifiers,  a  modification  of  the  above,  in  which  the  use  of  a  hydraulic 
joint  is  dispensed  with. 

(c)  Purifiers,  such  as  Green's  well-known  type,  in  which  small  sections  of  the 
cover  are  alone  removable.     These  are  fitted  with  dry  joints. 
All  the  above  groups  may  again  be  erected — 

(a)  At  ground  level,  or  partially  buried. 

(6)  Above  ground  level,  i.e.  overhead  types. 

So  far  as  the  'arrangement  of  the  purification  plant  is  concerned,  irrespective  of  the 
design  of  the  actual  vessels,  it  is  essential  to  provide  facilities  for  rapid  and  economical 
discharging  and  charging.  It  will  be  seen  at  once  that  where  ground  space  is  a  con- 
sideration the  overhead  system  should  be  decided  upon,  as  in  this  way  a  floor  space 
for  mixing  and  revivification  is  provided  beneath  the  vessels.  With  the  ground- 
level  system  a  special  preparing  floor  must  be  arranged  for  alongside  the  boxes. 
When  ground-level  or  sunk  purifiers  are  employed  they  usually  rest  on  a  plain,  flat 
slab  of  concrete.  The  nature  of  the  subsoil  should,  however,  be  carefully  ascertained, 
as  piling  or  other  methods  may  be  necessary  (see  page  31).  Overhead  types  are 
supported,  usually  from  10  to  12  feet  above  the  lower  floor,  on  cast-iron  columns  or 
steel  stanchions  braced  together  by  cross  girders,  which  provide  a  seating  for  the 
boxes. 

In  large  works  the  purification  plant  is  comparatively  costly,  but  some  outlay 
may  be  saved  by  arranging  the  vessels  so  that  they  butt  one  on  to  another,  with  one 


THE   DRY   PURIFICATION   OF   COAL   GAS          401 

division  plate,  thus  saving  a  side  plate  between  each  pair.     This  arrangement  applies 
to  dry-lute  purifiers  alone. 

With  overhead  purifiers  the  gas  outlets  are  often  constructed  in  such  a  mariner 
as  to  form  a  discharging  shoot  to  the  floor  below ;  in  this  way  the  spent  material 
may  be  easily  shot  to  the  lower  level  and  spread  out  in  layers  to  undergo  revivifi- 
cation. After  revivification  the  material  is  carried  up  to  the  upper  floor,  in  the 
smaller  works  by  manual  labour,  and  in  larger  works  by  some  form  of  lift,  elevator, 
or  crane.  With  overhead  purifiers  the  operation  of  discharging  and  recharging  may 
be  carried  out  in  a  half  or  a  third  of  the  time  required  with  ground-level  systems, 
where  a  considerable  amount  of  wheeling  to  and  fro  has  to  be  done.  Other  advantages 
of  the  overhead  types  are  that  they  are  very  much  more  accessible  for  painting  and 
repairs,  whilst  there  is  less  capital  outlay  on  land.  The  outstanding  merit  of  the 
ground-level  purifiers  is  their  comparatively  moderate  cost,  whilst  maintenance 
charges  are  lower,  owing  to  the  absence  of  heavy  girder-work  and  stanchions.  In 
cases  of  treacherous  subsoils  it  may  not  be  possible  to  adopt  the  overhead  type, 
owing  to  the  impossibility  of  concentrating  the  whole  load  on  small  areas  (i.e.  the 
bases  of  the  standards).  In  spite  of  their  good  features,  the  overhead  purifiers  are 
comparatively  rare.  The  explanation  probably  lies  in  the  fact  that  the  interest 
accruing  from  the  additional  capital  expenditure  involved,  combined  with  increased 
maintenance  costs,  would  probably  be  a  greater  item  than  the  saving  which  would 
be  effected  in  labour. 

THE   SIZE   OF   PURIFIERS 

It  is  essential  that  purifiers  should  be  of  ample  capacity  for  the  work  they  are 
called  upon  to  perform.  Nothing  is  more  detrimental  to  working  efficiency  than  an 
overloaded  series  of  purifiers,  and  the  cost  of  an  additional  unit  can  soon  be  expended 
in  labour  charges  owing  to  the  shorter  life  of  the  material  when  capacity  is  inadequate. 

For  oxide  purification  alone  it  will  suffice  if  the  following  allowance  is  adhered 
to— 

Set  of  four  purifiers  :  Allow,  as  a  minimum,  an  area  of  0-5  square  foot  per 
1,000  cubic  feet  of  gas  to  be  purified  per  day.  This  is  the  allowance  for  each  box,  and 
not  the  total  area  of  all  boxes.  If  lime  is  to  be  used  for  the  removal  of  sulphur  com- 
pounds, the  figure  should  be  increased  to  0-6  square  foot,  or  0-65  to  0-7  square  foot 
if  no  "  catch-boxes  "  are  available. 

So  far  as  the  total  area  of  all  boxes  is  concerned,  Hunt  states  that  for  lime  and 
oxide  purification  combined  20  to  30  square  feet  per  ton  of  coal  carbonized  per  day 
should  be  allowed. 

As  has  already  been  pointed  out  in  Chapter  I,  it  is  essential  to  make  provision 
for  future  requirements,  and  so  far  as  a  new  works  is  concerned  it  is  preferable  to 
erect  only  three  boxes  to  each  unit,  provision  being  made  for  the  easy  addition  of 
the  fourth  when  it  is  required.  In  such  cases  the  three  boxes  should  be  constructed 
with  a  capacity  50  to  60  per  cent,  larger  than  that  necessary  in  a  group  of  four ; 
that  is,  an  allowance  for  each  box  of  0-8  to  0-85  square  foot  per  1,000  cubic  feet  of 
gas  passing  per  day.  Considering  the  case  of  a  very  small  works  with  prospects,  it 

D  D 


402 


MODERN   GASWORKS   PRACTICE 


would  be  advantageous  to  provide  only  two  boxes  at  the  outset.  Each  box,  how- 
ever, should  be  of  large  capacity,  say  1-5  to  1-7  square  feet  per  1,000  cubic  feet  per 
day.  In  this  way  there  will  be  very  little  increase  in  first  cost  (as  compared  with  a 
system  of  three  small  purifiers),  and  money  will  be  saved  when  extensions  are 
carried  out. 

Within  certain  high  and  low  limits  purifiers  may  be  constructed  of  almost  any 
dimensions.  They  are  invariably  square  or  rectangular  in  shape.  The  minimum 
size  is  usually  4  feet  square  by  3  feet  in  depth,  whilst  the  maximum  size  will  not, 
except  in  abnormal  cases,  exceed  1,600  superficial  feet,  i.e.  boxes  having  sides,  of 
40  feet.  A  vessel  of  this  description  would  be  capable  of  dealing  with  about  2| 
million  cubic  feet  per  diem ;  consequently,  in  the  case  of  those  works  making  more 
than  this  quantity  of  gas,  it  is  necessary  to  split  the  stream  prior  to  reaching  the 
purifiers  and  to  treat  it  in  two  (or  a  number  of)  separate  units. 

The  body  of  a  purifier  is  invariably  constructed  from  cast-iron  plates,  bolted 
together,  the  joints  being  made  in  the  usual  manner  from  borings,  or  faced  and  red- 
leaded  (see  page  348).  On  the  other  hand,  it  is  essential  that  the  lid  of  the  vessel 
should  be  light,  to  which  end  it  is  built  up  from  steel  or  wrought-iron  plates  (usually 

J  inch  thick)  and  suitably  braced  with  rolled  steel 
sections.  Owing  to  the  necessity  of  maintaining  a 
clear  passage  for  the  cover  in  the  water-lute,  the 
flanges  of  purifier  plates  are  frequently  arranged  in  a 
somewhat  unconventional  manner.  The  construction 
of  the  lute,  showing  the  way  in  which  the  flange  changes 
over  from  the  exterior  to  the  interior,  and  the  method 
of  bolting  on  the  separate  lute  plate  and  the  base  plate, 
will  be  followed  from  Fig.  265.  It  should  be  noted 
that  in  the  case  of  a  ground-level  vessel  the  flanges 
would  be  internal,  and  not  external.  In  this  way  the 
o  1  joints  and  bolts,  being  inaccessible  from  below,  can 

be  attended  to  from  the  interior.  So  far  as  the 
thickness  of  the  cast-iron  plates  employed  is  con- 
cerned, the  following  figures  may  be  taken  as  satis- 
fying all  requirements — 


*J 


-*--«- 


FIG.  265. — PURIFIER  SIDE  PLATE 
(CAST-IRON). 


Purifiers  up  to  10  feet  square       .          .  f  inch  plates. 

„  „       20     „  „  .          .  ft      „         „ 

above  20     „  .    .          .  f 

Flanges  are  cast  y1^  inch  or  J  inch  thicker. 


The  common  methods  of  jointing  cast-iron  plates  together  are  described  and 
illustrated  on  page  348.  Side-plates  are  usually  cast  with  a  width  of  four  or  five  feet 
for  standardization. 

The  smallest  purifiers  are  usually  three  feet  deep,  and  the  largest  sizes  vary  from 
aix  to  eight  feet  deep.  Intermediate  sizes  are  four  to  six  feet  in  depth.  As  a  rule 


THE   DRY   PURIFICATION   OF   COAL   GAS          403 

for  ascertaining  the  required  depth  for  a  purifier,  the  author  suggests  the  following — 
Depth  in  feet  =  ^Total  superficial  area  X  !•! 

The  depth  may  then  be  taken  to  the  nearest  foot — portions  of  a  foot  being  neglected 
owing  to  the  general  practice  of  casting  these  plates  in  lengths  divisible  by  a  foot. 
For  smaller  purifiers,  that  is  boxes  with  an  area  up  to  300  square  feet,  multiply  by  1-3 
instead  of  1-1. 

Thus,  considering  a  purifier  30  feet  X  30  feet 

Total  area  =  900  square  feet 

#900  =  547  and  547  X  1-1  =  6-017  feet. 

Therefore  the  required  depth  is  six  feet. 

Again,  with  a  Smaller  purifier,  say  12  feet  X  16  feet 
Total  area  =  192  square  feet. 

#192  =3-725  and  3-725  X  1-3  =4-84  feet. 
Accordingly  required  depth  is  5  feet. 
/ 

PURIFIER   CONNECTIONS 

The  size  of  the  gas  main  working  in  connection  with  purifiers  may  be  best 
calculated  as  follows — 

Diameter  of  pipe  in  inches  =varea  of  each  box  in  square  feet.  For  small  puri- 
fiers (up  to  60  square  feet  area)  the  result  can  be  taken  as  it  stands,  but  for  medium 
size  boxes  deduct  one-sixth  and  for  large  boxes  one-fourth.  As  an  example,  con- 
sider a  square  purifier  with  40  feet  sides,  then — 

Diameter  of  pipe  in  inches  =  VI, 600    less  one-fourth 

40  —  (i  of  40) 
=     40  —  10  =  30  inches. 
i.e.  a  30-inch  main  would  be  used. 

Another  rule  which  may  be  conveniently  employed  is  that  due  to  Milbourne — 
Diameter  of  pipe  in  inches  = 

Length  and  breadth  of  purifier  (in  feet) 

-y-  X  0-7 

thus,  with  a  40-feet  square  purifier  we  get — 

4-^±i°  X  0-7  ^X  0-7  =28  inches. 
2  2 

In  such  a  case  it  would  be  decided  to  put  in  the  next  largest  standard  size  of 
main,  i.e.  a  30-inch,  pipe. 


404 


MODERN   GASWORKS   PRACTICE 


GENERAL   CONSTRUCTIONAL   NOTES 

Ordinary  water-lute  purifiers  are  constructed  from  side  plates  having  the  lute 
made  as  portion  of  the  plate  itself,  or  with  the  lute  as  a  distinct  casting  (Fig.  265). 
From  the  economical  standpoint  the  former  type  is  preferable,  first,  owing  to  the 
initial  outlay  being  less,  and  secondly,  on  account  of  the  greater  ease  with  which  it 
is  erected.  With  both  types  the  most  costly  section  is  the  corner  plate.  The  depth 
of  the  water  lute  (usually  half  the  depth  of  the  box)  is  an  important  consideration, 
and  it  must  be  ensured  that  the  depth  of  water  obtainable  will  be  sufricient  to  with- 
stand the  heaviest  pressure  which  is  likely  to  prevail  inside  the  vessel.  Covers  for 


FIG.  266. — MILBOURNE'S  COVER  FASTENER. 

purifiers  may  be  either  flat  or  curved.  In  either  case  some  form  of  trussing  or  stiffen- 
ing will  be  required,  and  strong  curbs  should  be  provided  when  the  vessel  is  of  any 
size.  So  far  as  lifting  is  concerned,  the  cover,  when  of  the  domed  type,  is  usually 
provided  with  a  stout  lifting-eye  attached  to  straps,  which  are  in  turn  riveted  to  the 
side  plates  and  again  to  the  bottom  curb.  With  the  flat  cover,  which  is  invariably 
employed  with  dry  lutes,  the  lifting  is  frequently  carried  out  by  means  of  eyes  attached 
to  the  external  stiffening  sections  or  trussing.  The  floor  plates  of  purifiers  should, 
when  possible,  have  internal  flanges,  thus  avoiding  local  stress  on  the  bottom  plates. 
The  box,  moreover,  when  of  the  ground-level  type,  obtains  a  level  bearing  on  the 
concrete  and  the  joints  are  readily  accessible.  The  plates  of  purifiers  should  be 
designed  with  as  few  different  patterns  as  possible,  whilst  an  eye  must  be  given  to 
the  avoidance  of  awkward  castings.  When  the  plates  are  large,  they  must  be 
adequately  stiffened.  Some  means  should  always  be  provided  for  by-passing  the 


THE   DRY   PURIFICATION   OF   COAL   GAS 


405 


separate  tiers  of  material  should  this  be  necessary  owing  to  abnormal  back-pres- 
sure.    Special  tier- valves  are  made  for  the  purpose,   although  a   mild-steel  plate 


FIG.  267. — MILBOURNE'S  COVER  FASTENER,  SHOWING  (a)  CATCHES  SHUT,  AND  (b)  CATCHES  OPEN. 

attached  to  a  rod  passing  through  a  stuffing-box  on  the  purifier  will  answer  the 
purpose  equally  well.      This  plate  lies  flat  on  the  grid,  and  is  not  covered  with  the 


FIG.  268. — "  ECLIPSE  "  COVER  FASTENER,  SHOWING  RUBBER  JOINT. 


purifying  material.     In  addition,  it  is  a  good  plan  to  have  a  pressure  cock  fitted  to 
each  layer. 

The  chief  advantages  of  the  dry-lute  purifiers  may  be  summarized  as  follows — 

(a)  Lower  initial  cost. 


406 


MODERN   GASWORKS   PRACTICE 


Fia.  269. — FASTENERS  FOR  LUTELESS  COVERS. 


(6)  Increased  safety,  owing  to  the  elimination  of  the  water  seal,  which  is  liable 
to  evaporate,  thus  lessening  the  seal. 

(c)  They  will  not  "  blow  "  in  the  event  of  a  temporary  excess  of  back-pressure. 

(d)  Greater  durability. 


THE   DRY   PURIFICATION   OF   COAL   GAS          407 

(e)  There  is  no  risk  of  frozen  lutes  in  winter,  with  the  consequent  absence  of 
anxiety. 

(/)  Owing  to  the  lighter  construction  of  the  lids,  the  lifting  apparatus  is  not  so 
cumbersome. 

There  are  several  types  of  jointing  material  made  use  of  with  luteless  purifiers. 
A  gas-tight  joint  is  ensured  by  a  strip  of  rubber  or  tallowed  hemp  inserted  between! 
the  flanges  of  the  cover  and  side  plates.  The  two  flanges  are  then  pulled  together  by 
ordinary  bolts  and  nuts  inserted  at  a  pitch  of  about  twelve  inches.  The  most 
effective  arrangement,  however,  is  an  automatic  catch  attached  to  a  shaft  running; 
throughout  the  length  of  the  side  of  the  box.  By  means  of  an  eccentric  movement, 
the  holding-down  catches  can  then  be  released  simultaneously  along  the  whole  side. 


FIG.  270. — MILBOURNE'S  JOINTING  FOB  DRY  LUTES. 

Milbourne's  fastener  is  illustrated  in  Figs.  266  and  267.  In  this  case  the  complete 
cover  is  released  from  one  point,  about  thirty  seconds  being  required  for  the  opera- 
tion. Special  fastener  clutches,  spaced  at  intervals  of  about  three  feet,  are  actuated 
by  eccentric  discs  attached  to  square  steel  rods  running  along  the  edge  of  the  cover 
and  connected  at  the  corners  by  bevel  gearing.  When  a  cover  is  unfastened  the  first 
portion  of  the  stroke  of  the  operating  lever  imparts  a  downward  vertical  motion  to 
the  fastener  clutch,  whilst  the  second  portion  of  the  stroke  swings  the  clutches  out  of 
position.  When  a  lid  is  tightened  up  the  reverse  occurs.  The  "  Eclipse  "  fastener  is 
shown  in  Fig.  268.  In  this  case  the  fastener  is  fixed  to  the  side  of  the  purifier,  the 
steel  shaft  running  beneath  a  raised  cast-iron  flange.  When  the  cover  is  released 
the  whole  of  the  catches  fall  clear,  and  leave  the  cover  a  free  passage  for  lifting. 
So  far  as  the  various  means  of  jointing  are  concerned,  the  main  difference  lies  in  the 
formation  of  the  rubber  strip  and  as  to  whether  it  is  applied  to  the  upper  or  lower 
curb.  Common  types  are  shown  in  Figs.  268,  269,  and  270. 


408 


MODERN   GASWORKS   PRACTICE 


LIFTING   GEAR 

In  small  works  the  cover  may  be  lifted  by  means  of  eyebolts  or  hooks  attached 
to  it,  with  pulley  blocks  running  on  a  horizontal  joist  overhead  and  supported  at 
each  end  by  columns  of  timber,  cast-iron  or  steel.  In  medium-sized  and  large 
works,  a  common  lifting-gear  is  that  composed  of  two  "  A  "  frames  running  on  rails 
on  either  side  of  the  purifiers.  The  apexes  of  the  two  "  A  "  frames  are  then  con- 
nected by  a  single  joist  or  a  lattice  girder.  Travelling  can  be  effected  by  hand,  a 
purchase  being  obtained  by  means  of  suitable  toothed  gearing.  The  actual  lifting 
of  the  cover  may  be  carried  out  by  pulley  blocks,  or  in  the  case  of  very  heavy  covers 
by  means  of  hydraulic  or  other  power.  Where  electric  power  is  available  an  over- 
head crane  of  the  shop  or  foundry  pattern  can  be  used  with  advantage. 

THE   PRESSURE   ON  PURIFIER   COVERS 

It  should  be  borne  in  mind  that  in  the  case  of  purifiers  with  a  water-luted  cover, 
the  internal  gas  pressure  on  the  box  and  cover  is  limited  by  the  depth  of  water  in  the 
seal.  The  pressure  which  the  cover  has  to  withstand,  therefore,  is  the  total  pressure 
of  the  gas  on  its  (the  cover's)  area,  less  the  weight  of  the  cover  itself.  Holding-down 
lugs  have,  therefore,  to  be  constructed  accordingly.  The  bracing  of  the  cover  must 
also  be  strong  enough  to  avoid  distortion  of  the  members,  with  its  consequent  ten- 
dency towards  leaking  rivets.  When  abnormal  pressure  occurs  the  lute  in  this  type 
of  purifier  forms  the  safety  valve,  and  the  seal  "  blows." 

In  dry-luted  covers  the  pressure  provided  for  must  be  greater,  and  a  normal 
specified  test  would  be  1 J  Ib.  per  square  inch,  i.e.  a  water  column  of  3  feet  6  inches. 
As  the  holding-down  bolts  are  closer  together  than  in  the  water-lute  purifier,  no 
difficulty  is  found  in  designing  them  of  sufficient  area  to  withstand  the  upward  tension. 
When  domed  tops  are  employed  the  pressure  is  less  than  with  the  flat  top,  and  an 
allowance  for  this  can  accordingly  be  made. 

PURIFIER   GRIDS 

The  most  usual  form  of  grid  employed  for  supporting  the  material  within  the 


FIG.  271. — OPEN-ENDED  PURIFIER  GRID. 


FIG.  272. — BUTT-ENDED  GRID. 


purifier  is  the  flat  sieve,  made  in  wood,  and  built  up  with  either  open  or  butt-ends, 
as  shown  in  Figs.  271  and  272.     Within  recent  years  there  has  been  some  tendency 


THE   DRY   PURIFICATION   OF   COAL   GAS 


409 


to  employ  grids  of  the  hurdle  type,  either  by  themselves  or  in  conjunction  with  the 
ordinary  flat  sieves.  The  chief  advantage  attached  to  such  grids  is  that  they  may, 
in  so"me  cases,  be  responsible  for  a  reduction  in  back-pressure,  but  it  seems  that  their 
advantages  are  almost  entirely  outweighed  by  their  defects.  Amongst  the  latter 
may  be  mentioned— 

(a)  The  tendency  of  the  gas  to  short-circuit  through  the  material. 

(6)  The  wear  and  tear  on  the  grids  is  greater. 

(c)  A  common  method  of  overcoming  back-pressure  in  an  ordinary  purifier  is 
by  drawing  a  slide  and  thus  by-passing  a  tier  of  the  material.     With  the  hurdle  grid 
this  cannot  be  done. 

(d)  The  operation  of  discharging  is  more  costly,  and  occupies  a  greater  length 
of  time. 

It  must  not  be  supposed,  however,  that  the  hurdle  grids  have  not  their  good 
points,  and  many  engineers  adhere  entirely  to  their  use.  For  the  plain  flat  sieve  the 
average  cost  is  about  6d.  per  square  foot,  in  normal  times. 


THE   COST   OF   PURIFIERS 

No  definite  figure  for  costs  based  on  the  capacity  per  1,000  cubic  feet  of  gas 
dealt  with  can  be  given,  owing  to  the  expenditure  per  unit 
volume  undergoing  considerable  reduction  as  the  capacity 
increases.  For  instance,  a  set  of  four  purifiers  complete  with 
connections,  lifting  crane,  etc.,  to  deal  with  100,000  cubic  feet 
of  gas  per  diem,  will  cost  about  £500,  i.e.  £5  per  1,000  cubic 
feet ;  whilst  a  similar  set  capable  of  taking  two  million 
cubic  feet  per  diem  will  run  into  rather  more  than  £4, SCO, 
i.e.  £2  5s.  per  1,000  cubic  feet.  These  figures  refer  to  dry- 
luted,  ground-level  boxes,  and  do  not  include  the  building. 
If  water- luted  boxes  are  under  consideration,  15  to  20  per 
cent,  may  be  added.  The  diagram  shown  in  Fig.  273  gives 
an  indication  of  the  manner  in  which  the  cost  varies  in 
accordance  with  the  capacity.  The  figures  include  con- 
nections, lifting  gear,  valves  and  foundations.  The  follow- 
ing table  shows  the  manner  in  which  the  outlay  is  distributed 
over  the  various  portions  of  the  installation  in  normal  cases  for 
medium-sized  plant — 


—6000 

3000  — 

2800  — 

- 

a 

01 

5 

2600  — 
2400  — 

—5000 

a 

0 

I 

2200  — 

nnnn 

1800  — 

0 

1 

0 

1600  — 

1400  — 

—  4000 

"o 

CO 

•0 

e 

1200  — 

—  3000 

3 
0 

1000  — 

H 

800  — 

,5 

600  — 

—  2000 

'o 

9 
a 
id 
O 

400  — 

- 

200  

—  1000 

—  i 

-  500 

Purifying  boxes 
Covers  (dry  lute) 
Lifting  apparatus 
Grids  (ordinary  flat  type) 
Connections  and  valves 


50  per  cent,  of  total  expenditure. 

15 

4  to     6 

6  to  10          „         „        „ 
20  to  30 


FIG.   273.  —  DIAGRAM  Castings  for  the  boxes,  etc.,  cost,  normally,  from  £10  to  £11 

SHOWING  APPROXIMATE  per  ton      ^he  covers  cost  from  £17  to  £19  per  ton,  or  the 
COST  OF  A  SET  OF  FOUR  . 

PURIFIERS.  whole  set,  including  connections,  from  £12  to  £lo  per  ton. 


410 


MODERN   GASWORKS   PRACTICE 


So  far  as  the  cost  of  buildings  is  concerned,  this  has  already  been  touched  upon 
in  Chapter  I.  If  a  steel-framed,  brick-panelled  structure  is  erected  the  cost  will 
amount  approximately  to  2%d.  per  cubic  foot  capacity,  including  foundations.  This 
type  of  building  is,  however,  rarely  employed,  and  the  modern  tendency  is  to  erect  a 
light  steel-framed  shed  carrying  a  roof,  but  open  at  the  sides.  Such  a  building 
may  be  estimated  at  Is.  Qd.  per  square  foot  of  area  covered. 

PURIFIER   VALVES 

The  valves  made  use  of  on  purifiers  are  commonly  of  three  distinct  types — 

(a)  Centre  valves. 

(6)  Separate  slide  valves  (such  as  the  well-known  rack  and  pinion  type). 

(c)  Hydraulic  valves. 

One  type  of  centre  valve  is  shown  in  Fig.  274.     This  valve  is  constructed  with 


— o 


SECTION    ON    LINE     G-H 


SECTION  ON  LINE    A-B  SECTION  ON   LINE   C'D 

FIG.  274. — DRY-FACED  CENTRE  VALVE. 

dry  faces,  and  enables  any  number  of  the  four  purifiers  to  be  in  action  at  one  time. 
It  is  claimed  that  with  valves  of  this  description,  as  the  faces  are  always  covered 
when  at  work,  no  deposit  of  any  kind  can  collect,  thus  leakage  from  one  valve  chamber 
to  another  is  precluded.  Hydraulic  centre  valves,  in  which  water  is  the  sealing 
medium,  are  also  employed,  but  the  ordinary  type  possseses  the  disadvantage  that 


THE   DRY   PURIFICATION   OF   COAL   GAS 


411 


it  will  only  operate  the  purifiers  in  one 
combination,  i.e.  any  three  boxes  at 
work  with  one  out  of  action.  The  con- 
struction of  the  centre  valve  is  some- 
what complex,  but  an  idea  of  the 
principle  may  be  obtained  from  the 
diagrammatic  representation  given  in 
Fig.  275. 

Walker's  type  of  rack  and  pinion 
valve  is  shown  in  Fig.  276,  whilst  the 
ordinary  single  water  valve  is  seen  in 
Fig.  277.  These  water  or  hydraulic 
valves  are  of  simple  construction  and 
consist  of  a  rectangular  cast-iron  box 
with  a  mid- feather  extending  to  within 
a  short  distance  of  the  bottom.  When 
water  is  admitted  to  the  box  the  gas 
way  is  stopped,  and  in  order  to  open 
the  gas  passage  the  water  is  merely  run 


No.   2 


No3 


No.  1 


Off 


FIG.  276. — RACK  AND  PINION  VALVE.  - 
WALKER'S  TYPE. 


FIG.  275. — DIAGRAM  SHOWING  PRINCIPLE  OF 
OPERATION  OF  CENTRE  VALVE. 


off  from  the  drain  pipe  at  the  base.      The 
depth  of  seal  employed  in  these  valves  is 
usually  the  same  as  that  in  the 
seal  of  the  purifier  cover. 

So  far  as  the  relative  advan- 
tages of  the  various  types  of 
valves  are  concerned,  the  follow- 
ing points  may  be  stated — 

(a)  Centre  valves.  Are  simple 
in  operation,  but  may  give 
trouble  owing  to  gas  leaking  from 
one  valve  chamber  to  another. 
If  this  occurs  a  portion  of  the 
crude  gas  may  get  through  to  the 
clean  gas  outlet  and  give  rise  to  a 
stain. 

(6)  Slide  valves.  These  may 
be  either  of  the  rack  and  pinion 
or  worm  and  rack  type.  They 
should  be  flanged  so  that  they 
may  be  readily  replaced  if  faulty. 
One  spare  valve  should  always 


412 


MODERN   GASWORKS   PRACTICE 


[Fie.  277. — COMMON  WATER  VALVE. 


to  accumulate  on  the  exposed  face,  thus  prevent- 
ing close  contact  between  the  disc  and  its  seat. 
The  method  under  notice  makes  the  grinding  in  of 
the  disc  a  very  simple  matter.  When  closing  a 
valve, when  the  disc  is  coming  in  contact  with  the  face 
of  the  valve,  the  small  lever  marked  "  A  "  is  swung, 
so  that  the  tooth  gears  into  one  of  the  recesses  on  the 
hand-wheel  marked  "  B."  This  action  locks  the 
spindle  and  disc  to  the  hand  wheel.  The  operator 
then  moves  the  handwheel  to  and  fro,  thus  revolv- 
ing the  disc.  The  lever  is  then  raised,  releasing 
the  spindle,  and  the  handwheel  is  turned  slightly, 
thus  tightening  the  disc  on  the  seat.  The  lever 
"  A  "  is  again  geared  with  the  handwheel,  and  the 
disc  further  revolved.  When  the  disc  is  fairly 
bedded  down,  the  lever  is  raised,  and  the  valve 
closed  home,  thereby  ensuring  that  the  faces  are 
in  complete  contact  and  the  valve  absolutely  gas- 
tight. 


be  kept  as  a  stand-by.     If  this  is  done   all   the 
valves  in  use  can  be  overhauled  in  turn. 

(c)  Water  valves.  These  valves  are  probably 
the  safest,  but  they  are  undoubtedly  cumber- 
some, and  decidedly  slow  in  action  in  comparison 
with  the  other  types.  The  latter  disadvantage  is, 
however,  not  of  paramount  importance  at  the 
present  day,  owing  to  the  extended  life  of  each 
purifying  vessel. 

A  novel  device  in  the  construction  of  purifier 
valves  is  the  "  Bearscot  "  patent  operating  gear 
(Fig.  278),  which  has  for  its  object  the  revolv- 
ing and  grinding  in  of  various  kinds  of  valve 
discs  upon  their 
seatings.  When, 
as  often  happens, 
valves  remain 
either  closed  or 
open  for  long 
periods,  tar,  sedi- 
ment, and  other 
undesirable  sub- 
stances are  apt 


FIG.  278.—"  BEARSCOT  "  VALVE 
OPEBATHTG  GEAR. 


THE   DRY   PURIFICATION   OF   COAL   GAS          413 

THE   COST   OF   PURIFIER   VALVES 

All  forms  of  purifier  valves  are  somewhat  costly,  this  applying  in  particular 
to  the  centre  types.  The  most  general  method  of  arriving  at  an  approximate  price 
for  valves  is  to  allow  so  many  pounds  (money)  per  inch  diameter  of  the  valve.  The 
following  may  be  taken  as  normal  figures  — 

Ordinary  rack  and  pinion  valve  .          .          .          .          .     £1  per  inch  diameter. 

Centre  valves      ........     £9  „  ,, 

Week's  centre  valve  and  such  types     .          .          .          .  £10  10s.          „  ,, 

PURIFYING   CAPACITY   OF   MATERIAL 

One  ton  of  good  quality  (Dutch)  bog-ore  may  be  considered  capable  of  removing 
the  sulphuretted  hydrogen  from  two  to  two  and  a  half  million  cubic  feet  of  gas  before 
it  is  finally  spent.  The  quantity  of  lime  required  to  extract  carbon  dioxide  varies 
in  accordance  with  the  amount  of  inert  matter  or  "  core  "  present  in  the  lime.  In 
the  usual  way,  from  3^  to  4  yards  are  necessary  per  million  cubic  feet  of  gas.  In  the 
case  of  lime  purification  methods  for  complete  removal  of  all  impurities  from  the  gas 
(i.e.  when  lime  is  used  in  conjunction  with  oxide),  the  quantity  of  lime  may  amount 
to  5J  cubic  yards  per  million  cubic  feet  of  gas. 

THE   REDUCTION   OF   SULPHUR   COMPOUNDS 

It  has  already  been  pointed  out  that  the  sulphur  compounds  remaining  in  coal 
gas  after  the  extraction  of  sulphuretted  hydrogen  consist  for  the  most  part  of  carbon 
disulphide,  which  is  present  to  the  extent  of  about  0-02  per  cent,  by  volume,  or  from 
25  to  50  grains  per  100  cubic  feet  of  gas.  The  carbon  disulphide  represents  about 
75  to  80  per  cent,  of  the  impurities  classed  as  "  sulphur  compounds,"  the  constitution 
of  the  remaining  7  to  10  grains  being  still  uncertain.  No  doubt,  from  60  to  70  per 
cent,  consists  of  thiophen,  whilst  it  seems  probable  that  the  remainder  is  partly 
accounted  for  by  ethyl  and  methyl  sulphides  and  certain  mercaptans. 

Processes  by  means  of  which  carbon  disulphide  may  be  partly,  or  in  some  cases 
wholly,  removed  may  be  summarized  as  follows  — 

(1)  Purification  by  means  of  sulphided  lime  (see  page  397). 

(2)  The  decomposition  of  CS2  by  heating,  as  in  the  Oregon  process. 

(3)  The  decomposition  of  CS2  by  heating  in  the  presence  of  a  catalyst,    such  as 
in  the  Carpenter-Evans  process. 

(4)  The  interaction  of  CS  2  with  certain  amino  compounds  such  as  aniline. 

(5)  The  liming  of  coal  in  the  retorts. 

'  (6)  The  absorption  of  CS2  by  means  of  alkalinated  cellulose,  as  in  the  "  Athion  " 
process. 

If  CS2  is  heated  to  a  suitable  temperature,  in  the  presence  of  hydrogen,  the 
following  reaction  will  occur  — 


This  reaction  is  the  basis  of  the  modern  systems  of  "  hot  "  purification,  but 
owing  to  the  extremely  small  quantities  in  which  CS2  is  present  in  coal  gas  it  is 
essential  that  the  reaction,  if  it  is  to  be  effective,  should  be  of  extremely  high  velocity. 


414  MODERN   GASWORKS   PRACTICE 

The  inception  of  purification  methods  on  these  lines  is  due  to  the  inventors  of  the 
Oregon  process,  who,  after  numerous  experiments  with  apparatus  which  proved 
unsuitable,  evolved  apparatus  very  similar  in  appearance  to  the  carburettor  of  a 
modern  water-gas  plant.  These  investigators  found  that  when  the  gas  was  passed 
through  a  vessel  containing  broken  firebricks  at  a  temperature  of  about  1,600°  Fahr., 
the  CS2  was  decomposed  into  sulphuretted  hydrogen  and  free  carbon.  The  plant 
employed  consisted  of  two  cylindrical  vessels  lined  with  fireclay  and  packed  with  fire- 
bricks laid  chequerwise.  The  vessels  were  heated  internally  by  the  combustion  of 
producer  gas,  and  whilst  one  was  being  heated,  the  second  was  purifying  the  gas,  and 
vice  versa.  That  is  to  say,  when  the  vessel  which  was  purifying  was  cooled  down  by  the 
inflowing  gas  to  a  temperature  at  which  its  efficiency  was  low,  the  operations  were 
reversed,  the  gas  being  diverted  to  the  second  vessel,  which  had  been  undergoing  a 
spell  of  reheating.  In  a  series  of  experiments,  extending  throughout  1909,  it  was 
found  that  the  average  reduction  in  the  quantity  of  sulphur  compounds  amounted  to 
71  per  cent.  In  a  process  of  this  description,  where  no  catalyst  is  employed,  tem- 
perature must  necessarily  play  an  important  part.  The  inventors  found  that  at 
800°  Fahr.  the  percentage  reduction  averaged  only  20-7  per  cent.,  whereas  at  1,300° 
Fahr.  it  might  be  so  much  as  76  per  cent.  The  cost  of  the  process,  including  all 
charges,  is  given  as  Q-5d.  per  1,000  cubic  feet  of  gas  treated. 

THE   CARPENTER-EVANS   PROCESS 

The  Carpenter-Evans  system  of  hot  purification  is  in  many  respects  similar  to 
that  described  above,  but  differs  in  one  very  important  particular,  and  that  is  the 
working  temperature  employed.  The  chemical  reaction  occurring  is  precisely 
similar  to  that  taking  place  in  the  Oregon  process,  but  the  velocity  of  reaction  is1 
greatly  increased  by  the  adoption  of  a  suitable  catalyst.  Consequently  extremes  of 
temperature  are  not  needed.  The  process,  which  is  now  assuming  some  importance 
in  this  country,  is  carried  out  on  the  following  lines  :  The  gas  is  first  heated  up  to 
about  770°  Fahr.  by  passage  through  tubular  heat-interchangers,  and  afterwards 
through  a  6-inch  tube  placed  within  the  furnace.  The  gas  then  passes  into  chambers 
containing  a  catalysing  agent,  wherein  the  carbon  disulphide  is  converted  into 
sulphuretted  hydrogen  and  free  carbon — 

CS2  +  2H2  =  2H2S  +C. 

The  catalytic  agent  employed  consists  of  fireclay  balls  about  1  inch  in  diameter 
impregnated  with  nickel  reduced  from  the  chloride,  the  apparatus  being  maintained 
at  a  temperature  of  about  800°  Fahr.  The  heated  gas,  on  leaving  the  catalyser, 
passes  through  a  special  heat  interchanger  in  which  it  gives  up  part  of  its  heat  to  the 
inflowing  cool  gas.  The  purified  gas  is  then  reduced  to  atmospheric  temperature, 
and,  finally,  the  sulphuretted  hydrogen  from  the  above  reaction  is  removed  by  oxide 
of  iron  in  the  usual  manner.  The  free  carbon  is  left  behind  in  the  catalysing  appar- 
atus, and  after  about  thirty  days'  run  it  is  necessary  to  remove  it.  This  is  done 
by  the  process  known  as  "  aeration." 

In  order  to  regenerate  the  material  of  any  distinct  unit  the  temperature  is  per- 
mitted to  drop,  and  air  is  pumped  at  a  definite  rate  through  the  tubes  containing 


THE   DRY   PURIFICATION   OF   COAL   GAS          415 

the  catalyst.  This  process  usually  occupies  about  a  week,  and  consists  in  burning 
out  the  deposit  of  free  carbon,  which  travels  away  as  C02.  During  the  first  four  days 
of  aeration  the  air  is  deprived  of  the  whole  of  its  oxygen.  When  once  oxygen  makes 
its  appearance  in  the  effluent  products  the  temperature  of  the  chamber  is  raised  to 
800°  Fahr.,  and  this  temperature  is  maintained  until  carbon  dioxide  ceases  to  be 
evolved,  when  the  process  is  complete.  Some  precaution  is  necessary  when  prepar- 
ing for  aeration,  or  when  recommencing  purifying  after  aeration  has  taken  place. 
The  tubes  will  contain  either  gas  or  air  as  the  case  may  be,  and  the  formation  of  an 
explosive  mixture  is  prevented  by  passing  in  a  current  of  inert  waste  gases  collected 
from  the  furnace  chimney.  In  this  way  the  gas  or  air  is  displaced  by  nitrogen  and 
carbon  dioxide.  The  original  activity  of  the  catalyst  is  immediately  restored  by  the 
aeration  process. 

E.  V.  Evans,  the  co-inventor,  has  pointed  out  that  in  a  system  of  this  kind 
it  is  necessary,  for  effective  working,  to  bear  in  mind  the  following  salient  points — 

1.  The  temperature  of  the  gas  should  be  raised  to  that  of  the  reaction  before 
coming  in  contact  with  the  catalyst. 

2.  There  must  be  a  sufficiency  of  surface  area  of  catalytic  material  exposed  per 
unit  volume  of  gas  passed. 

3.  The  reaction  is  affected  by  the  porosity,  specific  heat  and  thermal  conductivity 
of  the  porous  carrier  of  the  catalyst,  and  also  by  the  volume  of  free  space  allowed 
between  the  contact  surfaces. 

4.  The  presence  of  sulphuretted  hydrogen  in  the  gas  before  treatment  decreases 
the  efficiency  of  the  process,  which  cannot,  therefore,  be  advantageously  applied  to 
crude  gas.     It  seems  probable  that  carbon  oxysulphide  is  produced  by  conducting 
gas  containing  carbon  monoxide  and  sulphuretted  hydrogen  over  the  catalyst — 

(1)  SH2  =  H2  +  S  (2)  CO  +  S  =  COS. 

Ammonia  is  to  be  found  at  the  outlet  of  the  plant,  and  results  from  the  hydro- 
lysis of  hydrocyanic  acid,  which  occurs  on  the  lines  described  in  the  previous  chapter 
(see  page  378).  The  inventors  point  out  that  although  this  ammonia  is  too  small 
in  quantity  to  represent  a  financial  asset,  it  serves  a  useful  purpose  in  maintaining 
the  oxide  of  iron  used  to  remove  the  sulphuretted  hydrogen  (formed  by  the  decom- 
position of  the  CS2)  in  a  strongly  alkaline  condition.  Practically  the  whole  of  the 
oxygen  is  removed  by  the  process,  but  there  is  neither  increase  nor  decrease  in  the 
volume  of  gas.  So  far  as  the  effect  on  the  general  composition  of  the  gas  is  con- 
cerned, Dr.  Carpenter  has  given  the  following  figures — 

Before  After 

Analysis  of  Gas.                                                                                       Treatment.  Treatment. 

C02,  per  cent,  by  volume    .          .          ,          .          .          .          .1-44  1*45 

Heavy  hydrocarbons    .          .          .          .                    .          .                 3 '55  3-63 

Oxygen       .          .          .          ......          .          .       0-33  0-06 

Carbon  monoxide *       8*16  8-03 

Methane      .          .          .          . 26 -85  27 '26 

Hydrogen .    :      .          .          .     54-19  54-25 

Nitrogen ,         .          .          .          .       5-48  5-32 

Illuminating  power      ........        14-7  14-7 

Calorific  power,  B.Th.U.  gross 590-0  594-4 


416 


MODERN   GASWORKS   PRACTICE 


A  complete  view  of  the  plant,  with  explanation  of  the  working,  is  shown  in  Fig. 
279.  The  plant  illustrated  is  that  in  operation  at  the  East  Greenwich  works  of  the 
South  Metropolitan  Gas  Company  and  consists  of  five  units  each  capable  of  dealing 
with  three  million  cubic  feet  of  gas  per  day.  Each  unit  is  provided  with  a  producer 
(A)  and  a  combustion  chamber  (B)._  On  either  side  of  the  combustion  chamber  are 
the  heating  chambers  (C),  which  contain  the  reaction  tubes  (F).  The  gas  (purified 
from  8H2)  enters  the  plant  by  a  main  (H)  and  passes  into  the  heat  interchangers 
(G).  The  last-named  vessels  are  constructed  on  the  lines  of  a  multitubular  boiler, 


SCALC  or  FEET  SECTIONAL    ELEVATION 

FIG.  279. — THE  CARPENTER- EVANS  HOT  PURIFICATION  PLANT. 

A  Furnace,  B  Combustion  Chamber,  C  Heating  Chamber,  D  Collector  Tube,  F  Tubes  contain- 
ing Catalyst,  G  Heat  Interchangers,  H  Gas  before  treatment,  J  Gas  after  treatment,  K  Coke  Hopper, 
L  Coke  Handling  Plant. 

being  filled  with  3-inch  tubes.  The  hot  gas  leaving  the  plant  passes  through  the  heat 
interchangers  in  the  opposite  direction  to  that  of  the  inflowing  gas,  and  in  this  way 
gives  up  a  large  proportion  of  its  heat  to  the  cold  untreated  gas.  The  gas  is  further 
raised  in  temperature  in  the  heating  chambers,  and  then  flows  in  parallel  currents 
through  the  tubes  containing  the  catalyser,  passing  thence  to  the  collector  tube  (D) 
and  through  the  heat  interchangers.  After  undergoing  treatment  in  this  manner 
the  gas  will  usually  contain  about  20  to  30  grains  of  sulphuretted  hydrogen  per  100 
cubic  feet.  This  is  removed  by  a  series  of  secondary  purification  vessels  (two  in 
number  at  East  Greenwich)  containing  oxide  of  iron. 


THE   DRY   PURIFICATION   OF   COAL   GAS          41T 

According  to  Dr.  Carpenter  the  15  million  cubic  feet  plant  consumes  5|  tons  of 
coke  per  day  in  the  furnaces,  this  being  fed  into  the  producer  by  a  hopper  (K)  which 
receives  its  supply  from  a  telpher  (L).  The  average  cost  of  ridding  the  gas  of  its 
carbon  disulphide  in  this  manner  amounts  to  rather  less  than  one-third  of  a  penny  per 
1,000  cubic  feet.  The  expenditure  is  accounted  for  as  follows — 

Fuel  (coke  at  15s.  per  ton)      ....  0*099  pence  per  1,000  cubic  feet- 
Labour,  conveying,  clinkering,  etc.    .          .          .  0-058       „  „       „ 
Supervision       .......  0*011       „           „       „   . 

Power 0-003       „  „       „ 

Wear  and  tear 0-030       „  „       „ 

Interest  and  depreciation  (10  per  cent.)       .          .  0*098       ,,  „       „ 


Total         .     0-299      „          „       „ 

The  total  capital  expenditure  for  a  large  plant  is  in  the  neighbourhood  of  £1,500 
per  million  cubic  feet  per  day.  As  regards  efficiency  of  extraction,  the  proportionate 
reduction  is  somewhat  higher  when  a  gas  containing  a  larger  amount  of  CS2  is  dealt 
with.  The  following  results  illustrate  the  average  effect  obtained — 

Sulphur  Compounds — Grains  per  100  cubic  feet.  Reduction,  per  cent. 

Before.  After. 

63-78  ..          ..  10-34  ..          ..  83-8 

19-21  5-34  72-2     >- 


THE   ABSORPTION  OF   CS2  BY  AMINO   COMPOUNDS 

As  explained  beforehand,  carbon  disulphide  may  be  absorbed  by  means  of 
certain  compounds  such  as  aniline,  when  sulphuretted  hydrogen  is  evolved  and  a 
somewhat  complex  organic  residue  remains.  It  has  been  stated  that  the  reaction 
takes  place  on  lines  such  as  the  following — 

2C6H5NH2  +  CS2  =  (C6H5NH)2CS  +  H2S. 

The  carbon  disulphide  is  thus  precipitated  in  the  form  of  a  solid,  namely,  thio- 
carbanilide.      The  outstanding  difficulty  would  appear  to  be  the  loss  of  the  amino 
compounds  by  volatilization.     This  loss  may,  however,  be  curtailed  by  washing  the 
gas  with  weak  acids,  but  the  cost  of  the  process  renders  it  prohibitive  for  use  on  a . 
working  scale. 

THE   LIMING   OF   COAL 

The  treatment  of  coal  by  adding  lime  to  it  in  the  retort  is  by  no  means  novel, 
for  it  was  attempted  in  the  earliest  days  of  gas  lighting.  The  use  of  lime  for  this 
purpose  did  not,  however,  become  anything  like  general,  and  any  advantages  which 
may  result  from  the  process  seem  to  have  been  lost  sight  of  for  a  long  time,  until,  in 
1882,  W.  J.  Cooper  was  granted  a  patent  relating  to  the  treatment  of  coal  in  this 
way.  Cooper  claimed  substantial  advantages  for  his  system,  amongst  others  an 
enhanced  illuminating  power,  a  better  coke,  less  impurities,  and  more  ammonia. 

E  E 


418 

Present-day  interest  in  coal-liming  is  chiefly  attached  to  the  method  as  carried 
on  at  Cheltenham  Gas  Works,  and  with  which  the  names  of  R.  0.  and  J.  Paterson 
are  particularly  associated.  Liming  at  Cheltenham  was  first  practised  in  the  early 
eighties,  and  in  spite  of  the  repeal  of  the  sulphur  restrictions  in  1906,  the  process, 
though  dropped  for  a  time,  was  re-introduced  in  1910.  In  its  modern  form  the 
system  consists  in  admitting  to  the  coal,  just  prior  to  its  entering  the  breaker,  a 
small  proportion  of  caustic  lime.  In  order  that  the  liming  effect  may  be  uniform  a 
small  steam  jet  is  allowed  to  play  on  the  coal  as  it  falls  from  the  breaker.  In  this 
way  the  lime  is  fixed  to  the  surface  of  the  coal,  giving  each  small  particle  of  coal  a 
regular  coating.  A  further  quantity  of  steam,  introduced  at  the  overhead  retort- 
house  hoppers,  completes  the  fixing  process. 

So  far  as  results  are  concerned,  it  is  of  interest  to  note  that  at  Cheltenham  the 
sulphur  compounds  were  reduced  to  a  steady  average  of  about  21|  grains  per  100 
cubic  feet  of  gas.  The  yield  of  gas  per  ton  of  coal  advanced  by  over  SCO  cubic  feet, 
whilst  the  sulphate  of  ammonia  showed  an  increase  of  1-88  Ib.  per  ton  of  coal.  The 
quantity  of  lime  employed  varies  from  1-5  to  2  per  cent,  of  the  weight  of  coal  car- 
bonized, and  it  is  estimated  that  of  the  total  quantity  75  per  cent,  remains  behind 
in  the  coke. 

The  intermixture  of  lime  with  coal  is  adopted  on  gasworks,  not  with  a  view  to 
increasing  the  make  of  gas  and  other  products,  but  primarily  for  the  purpose  of 
curtailing  the  sulphur  compounds  in  the  finished  gas.  The  manner  in  which  this 
object  is  attained  is  not  wholly  understood,  the  reaction,  both  chemically  and  physic- 
ally, taking  place  on  extremely  complex  lines.  It  has  been  suggested  that  the 
addition  of  lime  is  followed  by  a  decrease  of  sulphur  compounds  in  the  gas,  but  a 
corresponding  increase  may  be  noted  in  the  sulphur  contents  of  the  other  products, 
chiefly  the  coke.  Possibly  the  presence  of  the  lime  merely  curtails  the  formation 
of  CS2,  the  gaseous  sulphur  being  evolved  almost  wholly  as  sulphuretted  hydrogen. 
Moreover,  if  CS2  were  evolved,  the  lime,  acting  as  a  catalytic  agent,  might  account 
for  its  partial  decomposition  into  SH2. 


THE   "ATHION"    PROCESS 

The  "  Athion  "  process  is  of  some  importance  so  far  as  Continental  practice 
is  concerned  ;  but  at  present  it  is  unknown  in  this  country.  The  gas,  after  being 
deprived  of  tar,  ammonia  and  sulphuretted  hydrogen,  is  washed  with  a  solution 
of  potassium  carbonate,  in  order  to  effect  the  complete  removal  of  carbon  dioxide. 
The  potassium  carbonate,  by  the  absorption  of  carbon  dioxide,  is  converted  into  the 
bicarbonate,  and  when  the  solution  of  the  latter  is  boiled,  the  salt  is  reconverted  into 
the  simple  carbonate,  carbon  dioxide  being  expelled.  The  potassium  carbonate 
solution  acts,  therefore,  in  a  continuous  cycle.  After  being  saturated  with  carbon 
dioxide  in  the  washers,  it  is  deprived  of  it  again  by  boiling,  cooled,  and  sent  back  to 
the  washers.  The  removal  of  C02  in  this  way  is  necessary,  otherwise  the  remainder 
of  the  process  for  the  extraction  of  the  sulphur  compounds  is  rendered  ineffective. 
The  carbon  disulphide  is  taken  up  by  the  "  Athion  "  material,  which  is  an  alkalinated 


THE   DRY   PURIFICATION    OF   COAL   GAS          419 

cellulose — that  is,  a  compound  of  alkali  and  cellulose,  obtained  by  treating  cellulose 
sulphite  with  soda  lye.  The  material  thus  produced  is  subjected  to  rolling  and 
crumbling,  afterwards  being  spread  on  purifier  grids  in  the  ordinary  manner.  The 
carbon  disulphide,  on  combining  with  the  material,  then  converts  it  into  xanthogenate 
of  cellulose  (viscose),  the  latter  product  being  of  use  in  the  manufacture  of  non- 
inflammable  celluloid.  The  inventors  claim  that  with  English  coal  the  sulphur  com- 
pounds are  reduced  from  30-75  to  7-87  grains  per  100  cubic  feet,  or  a  reduction  of 
75  per  cent.  Ten  tons  of  the  special  material  absorb  IJtons  of  carbon  disulphide, 
and  it  is  thus  calculated  that  10  tons  would  purify  35,000,000  cubic  feet  of  gas 


CHAPTER   XVII 
THE  STORAGE  OF  GAS 

OF  the  various  portions  of  apparatus  commonly  found  on  gasworks,  that  made  use 
of  for  storing  the  finished  gas  prior  to  its  delivery  to  the  supply  area  accounts  for  the 
greatest  individual  outlay.  In  normal  instances,  from  one-quarter  to  one-third  of 
the  total  capital  expenditure  on  the  works  will  be  absorbed  by  the  storage  plant, 
whilst  the  ground  area  covered  by  this  plant  will  amount  roughly  to  some  20  per 
cent,  more  than  that  required  for  retort  houses  and  coal  stores  combined. 

Since  the  introduction  of  gas  as  an  illuminant  the  same  principle,  that  of  a  floating 
vessel  rising  and  falling  in  a  seal  of  water,  has  been  embodied  in  all  storage  appara- 
tus ;  and  although  suggestions  for  replacing  the  gasholder  by  some  less  cumbersome 
contrivance  have,  from  time  to  time,  been  brought  forward,  they  have  not  as  yet 
materialized  in  practice. 

The  quantity  of  gas  which  it  is  desirable  to  hold  in  reserve  at  the  works  is  chiefly 
dependent  upon  the  fluctuation  of  the  daily  load  curve.  During  recent  years  the 
hourly  consumption  has  tended  to  become  more  and  more  regular,  with  a  consequent 
levelling  out  of  the  curve.  For  this  reason,  the  necessary  holder  capacity  has  under- 
gone reduction  ;  and  it  has  been  suggested  that,  in  the  future,  storage  will  be  prac- 
tically unnecessary,  once  the  daily  curve  of  consumption  has  been  straightened  out 
altogether.  It  must  be  remembered,  however,  that  one  of  the  most  important 
functions  of  the  gasholder  is  the  provision  it  affords  against  breakdown,  and  it  would 
seem  that  the  day  of  gasworks  without  this  familiar  apparatus  is  still  far  distant. 
With  present- time  conditions  it  may  be  assumed  that  the  maximum  hourly  consump- 
tion is  approximately  arrived  at  by  dividing  the  maximum  daily  output  by  22.  The 
amount  of  storage  provided  will  not  only  be  influenced  by  the  nature  of  the  supply, 
that  is,  whether  chiefly  lighting,  power  or  cooking,  but  by  the  facilities  at  the  works 
for  meeting  fluctuating  demands  with  a  similar  variation  in  the  quantity  of  gas 
produced. 

It  is  in  the  latter  respect  that  a  water-gas  plant,  capable  of  being  started  up  or 
dropped  at  short  notice,  proves  of  value.  Accordingly,  in  instances  where  the  daily 
load  curve  is  moderately  constant,  and  where  the  peak  of  the  load  may  occur  during 
the  daytime,  the  storage  provided  may  be  safely  reduced  to  16  or  18  hours'  maximum 
production.  On  works  in  which  no  surplus  water-gas  plant  (or  no  water-gas  plant 
at  all)  is  available  the  capacity  of  the  holders  should  be  increased  to  from  21  to  24 
hours'  maximum  "  make."  As  has  already  been  pointed  out  in  Chapter  I,  storage 
capacity  on  the  daily  "  make  "  basis  is  decidedly  elastic  ;  for  when  an  extra  holder 

420 


THE   STORAGE   OF   GAS 


421 


is  erected  on  a  works,  it  is  invariably  the  largest.  Consequently,  before  the  new 
holder  is  put  into  operation  the  storage  is  deficient ;  whilst,  once  it  is  at  work,  the 
storage  may  be  excessive,  provision  being  made  for  the  future. 

When  building  a  new  works,  or  when  adding  to  the  capacity  of  an  older  works, 
it  should  be  borne  in  mind  that  future  development  must  be  expected,  and  that  the 
most  ready  and  economical  way  of  meeting  this  is  to  make  arrangements  for  the 
addition  of  a  further  (outer)  lift  in  the  future.  The  holder  tank  in  such  cases  is 
constructed  of  sufficient  size  to  contain  the  extra  lift,  and  in  this  way  capacity  may 


«:        .   -       •.    *^. 


FIG.  280. — TELESCOPIC  HOLDER  WITH  BRACED  Gv IDE-FRAMING. 

be  increased  by  from  50  to  100  per  cent,  for  a  comparatively  small  outlay.  If  the 
holder  is  of  the  ordinary  guided  type  the  top  section  may  be  converted  into  a 
"  flying-lift  "  when  the  new  bottom  lift  is  added,  or,  alternatively,  the  guide-fram- 
ing may  be  carried  up  to  suit.  For  this  reason  the  spirally  guided  holder,'  ha,ving 
no  distinct  guide  framing,  lends  itself  more  readily  to  extension,  although  prior  to 
the  insertion  of  the  extra  lift  the  tank  will  be  subjected  to  additional  stressing  owing 
to  the  increased  "  overhang  "  of  the  guide  roller  carriages.  Needless  to  say,  the 
effect  of  this  loading  should  be  carefully  considered  when  the  tank  is  being  designed. 
The  addition  of  an  extra  lift  cannot  be  contemplated  if  the  holder  represents  the 


422 


MODERN   GASWORKS   PRACTICE 


principal  storage  unit,  for  the  time  required  to  complete  the  alteration  would  be 
at  least  from  five  to  six  weeks,  and  might  amount  to  three  or  four  months. 

THE   VARIOUS   TYPES   OF   GASHOLDERS 

The  chief  distinction  between  the  various  forms  of  holders  is  to  be  found, 
not  so  much  in  the  formation  of  the  floating  bell  but  in  the  manner  adopted  for 
guiding  the  bell,  and  in  the  construction  of  the  tank  containing  the  water.  The 
function  of  the  water  is  primarily  that  of  providing  an  elastic  gastight  seal  in  which 


FIG.  281. — TELESCOPIC  HOLDER  WITH  FLYING  LIFT. 

the  bell  may  rise  or  fall ;  in  addition,  it  receives  the  whole  of  the  pressure  thrown 
by  the  weight  of  the  bell,  and  in  this  way  forms  the  necessary  resistance  by  means 
of  which  the  bell  is  raised  or  the  gas  expelled. 

In  the  first  instance  gasholders  may  be  generally  classified  under  two  distinct 
headings : — 

1.  Simple  holders,  in  which  the  bell  consists  of  one  section  or  "lift"  only. 

2.  Compound  holders,  in  which  the  bell  is  composed  of  two,  or  a  number  of 
"  lifts,"  arranged  to  telescope  one  into  another  when  the  holder  is  empty,  or 
partly  so. 


THE   STORAGE   OF   GAS 


423 


More  broadly  classified,  the  various  descriptions  of  holders  may  be  set  down  as 
follows  :— 

1.  Holders  guided  by  wire  cables. 

2.  Holders  guided  by  ordinary  distinct  vertical  guide- framing,  with  or  without 
"  flying  lifts." 

A  typical  holder  with  braced  guide- framing  is  shown  in  Fig.  280.     A  telescopic 
holder  with  "  flying  "  lift  is  seen  in  Fig.  281. 


FIG.  282. — SPIRALLY  GUIDED  HOLDER. 


3.  Spirally  guided  holders  (left  or  right  hand,  or  a  combination  of  both).     The 
guides,  so  far  as  the  bell  is  concerned,  may  be  either  internal  or  external.     Fig.  282 
shows  a  spirally  guided  gasholder. 

4.  Holders  with  a  floating  roof,  generally  known  as  the  Nuremberg  type. 
The  cable-guided  holder,  though  of  historical  interest,  can  scarcely  be  con- 


424  MODERN   GASWORKS    PRACTICE 

sidered  under  the  heading  of  modern  structures.     Holders  of  this  type  are  still  in 
use,  the  largest  of  the  kind  being  in  operation  at  Middlesbrough. 

This  holder  has  three  lifts  (the  outer  of  which  is  185  feet  in  diameter)  and  a  total 
capacity  of  2 £  million  cubic  feet.  Theoretically,  at  least  three  cables  are  necessary 
for  a  single-lift  holder.  One  extremity  of  each  is  attached  to  the  upper  edge  of  the 
tank,  the  cable  is  then  led  round  a  pulley  fixed  to  the  top  curb  of  the  gasholder  and 
afterwards  passes  over  the  top  of  the  bell  to  a  second  pulley  attached  to  the  top 
curb  at  a  distance  of  about  one-third  of  the  circumference  from  the  first  pulley. 
The  cable  is  then  led  downwards  and  around  a  third  pulley  fitted  to  the  bottom 
,curb  of  the  holder,  its  other  extremity  being  fastened  to  the  top  of  the  tank.  Thus, 
&s  the  bell  rises  or  falls  each  cable  is  maintained  in  a  taut  condition. 

THE   DESIGN   OF  GASHOLDERS 

By  far  the  most  common  type  of  gasholder  is  the  single  or  multiple  "  lift " 
vessel  guided  by  a  number  of  columns  spaced  circumferentially  around  the  top  of 
the  tank  at  distances  of  from  15  to  30  feet  apart.  The  columns  are  adequately 
braced  together  by  horizontal  girders  and  diagonal  ties,  the  girders  for  large  holders 
being  built  up  from  steel  sections,  whilst  the  ties  (which  are  in  tension  only)  may  be 
made  from  plain  round  or  flat  steel  bars.  In  the  past,  it  was  customary  to  erect 
massive  cast-iron  columns  which  carried  a  guide  rail  and  ensured  the  rigid  guiding 
of  the  holder.  A  heavy  cast-iron  or  a  wrought-iron  trellis  cross  girder  extended 
from  apex  to  apex  of  the  columns,  whilst  tie-rods  of  unusual  length  completed  the 
framework.  To-day,  the  cast-iron  frame  has  been  entirely  superseded  by  that 
composed  of  comparatively  light  columns  constructed  from  rolled  mild- steel  sections. 
For  the  smaller  holders  (say  up  to  750,000  cubic  feet  capacity)  the  standards  may 
advantageously  be  plain  H  joists  at  centres  of  from  15  to  18  feet,  stayed  up  by  a 
smaller  size  of  the  same  section  for  the  horizontal  cross  struts.  Each  panel  would 
then  be  tied  together  by  circular  rods  arranged  diagonally,  and  meeting  in  the  centre 
of  the  panel.  At  the  junction  of  the  ties  a  centre  ring,  permitting  of  adjustment, 
may  be  used,  but  modern  practice  tends  towards  adjustment  at  the  standards. 
•Centre  rings,  moreover,  are  inclined  to  spring,  and  are  often  absurdly  weak  in  com- 
parison with  the  bars.  Particulars  of  the  guide  framing  for  a  holder  of  this  kind  are 
.given  in  Fig.  287  (page  433). 

For  larger  holders  the  necessary  size  of  a  single  rolled  section  for  the  upright 
stanchion  would  not  conduce  towards  economy  or  comeliness ;  accordingly,  it  is 
customary  to  build  up  the  columns  on  the  principle  of  the  lattice  girder,  the 
horizontal  cross-girders  being  designed  on  the  same  lines.  As  a  general  rule,  it  may  be 
said  that  single  H  joists  may  be  used  for  the  vertical  columns  so  long  as  their  depth 
is  not  found  (after  the  necessary  calculations  for  stability  have  been  made)  to  exceed 
18  inches.  When  joists  are  employed  their  total  height  from  tank  level  should  not 
toe  greater  than  65  times  their  cross- sectional  depth. 

THE   PROPORTIONS   OF   GASHOLDERS 

The  preliminary  operations  in  designing  a  gasholder  are  to  ascertain  the  required 
-capacity ;  and,  this  being  done,  to  determine  upon  the  diameter  and  height  of  the 


THE    STORAGE   OF   GAS  425 

bell,  the  number  of  lifts,  etc.  In  calculating  the  capacity  of  holders  the  space 
enclosed  by  the  domed  top  is  neglected,  owing  to  the  fact  that  the  gas  in  this  portion 
is  never  expelled.  The  volume  enclosed  by  the  domed  space  is,  therefore,  ineffective. 
For  preliminary  calculations  the  size  of  the  holder  may  be  arrived  at  by  applying 
the  simple  formula  :— 

Capacity  in  cubic  feet  =  -7854  X  (diameter)2  X  height. 

For  a  single-lift  holder  this  calculation  will  suffice,  but  when  a  multiple-lift  holder 
is  under  consideration  the  capacity  of  the  separate  lifts  should  be  distinctly  estimated 
by  applying  the  above  rule  to  each  section,  due  allowance  being  made  for  the  cups. 

CONSIDERATIONS  AFFECTING  THE  PROPORTIONS  OF 
GASHOLDERS 

There  are  many  factors  by  which  the  general  proportions  of  gasholders  are 
influenced.  Chief  amongst  these  are  :  — 

(a)  The  nature  of  the  sub-soil,  and,  therefore,  the  design  of  the  tank. 

(6)  The  ground  space  available  for  construction. 

(c)  The  pressure  required  to  be  thrown  by  the  holder  if  "  boosting  "  is  not  to 
be  resorted  to. 

If  the  ground  space  available  is  unlimited  the  constructor  is  not  tampered  in 
having  to  curtail  diameter,  with  a  consequent  increase  in  height,  although  deep 
lifts  may  be  necessary  in  order  to  obtain  the  necessary  pressure.  Deep  lifts  give 
rise  to  more  costly  tanks,  although  a  saving  may  be  effected  by  arranging  for  one 
lift  less  than  the  number  which  might  ordinarily  be  inserted,  thus  economizing  on 
the  total  number  of  cups  and  grips,  these  accounting  for  a  considerable  item  in  the 
outlay.  When  the  erection  of  a  holder  is  contemplated,  it  is  an  excellent  plan  to 
consider  two  suitable  propositions  entailing  different  proportions,  with  a  view  to 
taking  out  quantities  for  both.  The  following  figures,  which  show,  very  approxi- 
mately, the  weight  of  metal  employed  in  the  construction  of  two  types  of  gasholders 
of  identical  capacity  (1|  million  cubic  feet),  will  serve  to  illustrate  the  point  :  — 

Four-lift  Holder.     Three-lift  Holder. 
Depth  of  top  lift 
Ratio  -  ......         0-18  0-21 

Diameter 


„      T°tal  .         0-64  0-50 

Diameter 

Weight  of  steel  tank      .......  336  tons  405  tons 

„  crown  rest  framing          .....  52     „  63     „ 

guide  framing         ......  230     „  223     „ 

Total,  tank  and  framing          ......  618  tons  691  tons 


Top  lift  .  128  tons  146  tons 

Second  lift     .          .          . 68     „  80*   „ 

Third  lift  .                    .                              .       68     „  74     .. 

Fourth  lift     .  .                             .          .                    .  60     „ 

Weight  of  bell 324  tone  300  tons 

Total  weight .  942     „  991 


426  MODERN   GASWORKS   PRACTICE 

It  will  be  seen  that  the  four-lift  holder  shows  some  considerable  saving,  chiefly 
in  the  construction  of  the  tank,  in  weight  of  metal,  and  therefore  in  expenditure. 

The  depth  and  diameter  of  the  various  lifts  of  gasholders  are  readily  arrived 
at  by  any  one  of  experience,  the  following  being  the  usual  proportions  adhered  to  : — 

RATIO  OF  HEIGHT  TO  DIAMETER  OF  HOLDER 

For  single-lift  holders  the  height  varies  from  0-3  to  04  of  the  diameter.  With 
telescopic  holders  the  normal  proportion  varies  between  0-6  to  1-0  of  the  mean 
diameter.  In  both  cases  the  figure  given  refers  to  the  height  of  the  bell  only,  and 
does  not  include  the  depth  of  the  tank. 


Each  lift  will  be  approximately  of  similar  depth  ;  i.e.  the  depth  of  each  is  equal 
to  the  total  height  of  the  bell  divided  by  the  proposed  number  of  lifts,  due  allowance 
being  made  for  the  depth  of  cups  and  grips. 

DIAMETER  OF  LIFTS  AND  SIZE  OF  CUPS 

For  the  smaller  holders  the  width  of  the  cups  should  be  8  inches.  Medium  sized 
and  larger  holders  are  preferably  provided  with  a  10-inch  cup,  although  in  the  case 
of  the  largest  sizes  12  inches  is  occasionally  found.  It  will  be  understood  that  the  dia- 
meter of  the  second  lift  is  greater  than  the  diameter  of  the  top  lift  by  an  amount  equal 
to  three  times  the  width  of  the  cup  ;  the  diameter  of  each  succeeding  lift  increasing 
by  the  same  amount.  The  depth  of  the  cups  must  be  such  as  to  carry  a  water  seal 
sufficient  to  withstand  the  maximum  pressure  thrown  by  the  holder.  In  general, 
it  may  be  said  that  no  telescopic  holder  would  be  provided  with  cups  less  than 
16  inches  deep,  whilst  for  the  largest  holders  the  figure  would  not  exceed  24  inches. 

EISE  «OF  CROWN 

The  rise  given  to  the  domed  crown  of  a  holder  varies  in  accordance  with  the 
stresses  induced  ;  the  greater  the  rise,  the  stronger  the  crown.  The  dome  should 
in  all  cases  conform  to  a  segment  of  a  sphere.  Normally,  the  rise  will  lie  between 
T5  to  277  °f  tne  diameter  (though  seldom  TV),  a  greater  pitch  being  given  when  no 
trussing  is  employed.  The  cubic  capacity  of  the  crown  space  may  be  found  as 

follows : — 

/  3D2\ 

Volume  (in  cubic  feet)  =  0-5236  R  (  R2  +  —  J 

Where  R  =  Rise  of  crown  in  feet 
and      D  —  Diameter  of  holder  in  feet  (top  lift). 

PROPORTIONS  OF  LIFTS 

The  ratio  of  the  depth  of  a  lift  to  its  diameter  varies  to  some  considerable  extent, 
but  it  has  been  laid  down  by  Cripps  as  a  working  principle  that  the  depth  of  the 
lift  must  never  be  less  than  one-seventh  of  its  diameter,  otherwise  tilting  is  extremely 
likely  to  occur.  In  ordinary  practice  the  proportion  varies  from  one-fourth  to  one- 
fifth  of  the  diameter. 


THE   STORAGE   OF   GAS 


427 


THE   GUIDE-FRAMING   OF   GASHOLDERS 

The  author  takes  this  opportunity  of  pointing  out  that  the  knowledge  we  have 
of  the  stresses  and  strains  in  gasholder  structures  at  the  present  day  is  almost  solely 
built  up  from  the  theories  expounded  by  the  late  Sir  Benjamin  Baker  and  by  Mr.  F. 
Southwell  Cripps.     The  latter  has  published  an  eminently  practical  and  scientific 
treatise- — now  unhappily  out  of  print — which  has  for  long  been  and  still  remains  the- 
standard  work  of  reference  on  the  subject.     The  treatment  adopted  by  the  author 
in  the  following  pages — so  far  as  the  stresses  in  the  guide-framing  and  top  curb  are- 
concerned — is,  for  the  most  part,  a  reiteration  of  the  deductions  and  methods  of  Mr. 
Cripps,  as  set  forth  in  his  work  entitled,   "  The  Guide-framing  of  Gasholders,  and 
other  papers  chiefly  relating  to  the  strains  in  structures  connected  with  Gas- Works." 

The  stresses  occurring  in  the  guide-framing  of  a  gasholder  are  occasioned  by  pres- 
sure of  wind  and  snow.  The  weight  of  the  members  themselves  will,  however,  give 
rise  to  certain  loading,  and  this  effect  must  not  altogether  be  neglected.  In  calcula- 
tions of  the  kind  it  is  customary  to  assume  a  wind  pressure  equal  to  a  maximum  of 


-1 


I 


3 


^SUtUlr 


FIG.  283. — EADIAL  GUIDE  ROLLER. 


FIG.  284. — TANGENTIAL  GUIDE  ROLLEKS. 


32  Ib.  per  square  foot,  but  owing  to  the  surface  on  which  the  pressure  is  received 
being  rounded,  the  usual  50  per  cent,  reduction  may  be  assumed — thus  giving  an 
effective  pressure  of  16  Ibs.  per  square  foot  on  the  diametrical  projection.  Primarily 
it  must  be  understood  that  the  wind  and  snow  pressure  is  received  by  the  holder 
bell,  and,  by  means  of  the  guide- rollers,  it  is  transmitted  to  the  upright  standards, 
which  are  braced  together  in  such  a  manner  as  to  withstand  distortion  and  any 
tendency  to  capsize.  The  manner  in  which  the  stresses  are  transmitted  to  the 
framing  is  chiefly  dependent  upon  the  system  of  guide-rollers  adopted  ;  i.e.  whether 
the  rollers  are  radial,  tangential,  or  a  combination  of  both.  The  ordinary  radial 
roller  is  shown  in  Fig.  283.  Fig.  284  shows  a  combination  of  the  radial  and  tangential 
methods. 

For  the  purposes  of  calculation,  the  whole  of  the  guide-framing  may  be  regarded 
an  an  immense  cylinder,  receiving  partial  stiffening  from  a  light  internal  ring  (the 
bell  itself).  If  we  consider  a  simple  holder  with  radial  guide  rollers  subjected  to 
wind  pressure  in  one  direction  it  is  plain  that  there  is  a  tendency  for  the  bell  to  press 
hard  up  against  those  columns  on  the  leeward  side.  Owing  to  the  provision  of 


428  MODERN   GASWORKS   PRACTICE 

horizontal  struts  and  diagonal  ties  between  the  columns  this  stress  is,  in  the  modern 
form  of  holder,  transmitted  throughout  the  whole  framework,  and  not  merely  to  a 
portion  of  it.  If  tangential  rollers  are  employed  in  addition  to  radial  guides  the 
pressure  will  come  directly  on  to  about  one-half  of  the  total  number  of  columns  ;  but 
when  radial  rollers  alone  are  used,  one-quarter  of  the  columns  must  be  considered  as 
directly  loaded.  As  stated  above,  however,  the  remainder  of  the  framework  will, 
indirectly,  be  taking  its  share  of  the  load. 

As  the  vertical  columns  are  fixed  at  one  end  only  (i.e.  to  the  top  of  the  tank) 
the  whole  framing  may  be  looked  upon  as  a  girder  acting  in  the  capacity  of  a  huge 
'cantilever.  A  simple  cantilever  when  loaded  tends  :— 

1.  To  shear  off  at  the  point  of  support. 

2.  To  undergo  distortion  due  to  the  bending  moment.     Hence,  the  vertical 
•columns  have  a  tendency  : — 

1.  To  shear  off  at  the  base  and  overturn. 

2.  To  bend  and  become  distorted,  thus  causing  some  deformation  of  the  true 
•cylindrical  form  of  the  guide-framing. 

The  first  condition  applies  to  the  frame  structure  as  a  whole,  whilst  the  second 
affects  each  column  individually  in  accordance  with  the  wind  pressure  on  any 
particular  section. 

The  general  proportions  and  scheme  of  design  (such  as  height,  diameter,  and 
probable  number  of  standards)  of  the  holder  being  known,  the  first  step  in  the 

calculations  is  that  of  determining  the  maxi- 
mum stress  likely  to  be  met  with  in  each 
standard. 


WIND  PKESSUKE 

Consider  a    common    form    of 
having  guide-framing  extending    to    the    full 
height  of  the  bell. 

Let  L  —  total  length  of  columns,  which  in 
this  case  is  the  same  as  the  height  of  the  bell  (in  feet). 
Let  D  =  mean  diameter  of  bell  (in  feet). 

?>    P=Wind  pressure  (total  force)  in  Ibs. 

The  wind  pressure  P  acts  at  the  centre  of  pressure  of  the  bell,  i.e.  at  a  distance 
half-way  up  from  the  base.     Therefore,  the  overturning  moment 


but  P  =  total  wind  pressure. 

I.e.  16  Ibs.  per  sq.  foot  on  an  area  of  L  X  D  sq.  feet 
.-.  P=16LD 

L 

or,    the   overturning   moment  =  16LD  X  --  =  8L2D. 


THE   STORAGE   OF   GAS 

This  moment  is  resisted  by  the  reactionary  force  R  at  the  top  of  the  guide 
framing,  and  the  moment  of  the  reaction 

/.  R  X  L=8L2D 

8L2D 

or  R  =  -  =  8  L  D 

i.e.  the  overturning  force  due  to  the  wind  amounts  to  8  LD. 


SNOW  PRESSURE 

Snow  pressure  may  be  considered  equal  to  5  Ibs.  per  square  foot  on  one- fourth 
of  the  area  of  the  dome,  and  acting  at  a  point  of  one-sixth  the  diameter  from  the  top 
curb. 

Then  if  Ws  =  the  total  weight  of  snow,  this  acts  at  a  distance  of  —  from  the 

6 

edge,  or  —  from  the  centre  of  the  bell. 


To  find  total  weight  of  snow  : — 

Total  area  of  dome=  -7854D2 

/.  Portion  covered  bv  snow  = 


•7854  D2 


.  ,.     ,  -7854  D2  ^  _ 

or  weight  ot  snow  =  —  X  o 

=  -981  D2  Ibs. 


(0-981  is  very  nearly  1,  and  for  the  purposes 
of  calculation  Cripps  considers  that  it  may  be 
assumed  equal  to  1.) 

Therefore,  total  weight  of  snow=D2  Ibs. 

Now  the  snow  gives  rise  to  a  tilting  moment. 

Ws  X  ~    =  D2  X  r 
o  o 


or 


FIG.  286. 


This  moment  is  resisted  by  the  reaction  Rs  at 
the  top  of  the  columns,  and  the  moment  of  the  reaction  =  Rs  X  L 

D3 


or  Rs  — 


D! 
:3L 


430  MODERN   GASWORKS    PRACTICE 

Considering  the  results  of  wind  and  snow  together  we  see  that  the  total  reaction 
in  the  structure,  fhat  is  the  total  force  it  has  to  resist  is  : — 

D3 
SLD-fc-    - 

Accordingly,  the  bending  moment  on  the  structure  will  amount  to 


and  the  section  modulus  must  be  made  of  such  dimensions  as  to  withstand  this 
bending  moment. 

The  sectional  dimensions  of  the  columns  are  calculated  from  the  well-known 
formula 

Bending  moment  =  /  max  Z 

where  /  max  is  the  maximum  allowable  stress  in  the  steel,  i.e.  6  tons  per  square  inch 
for  ordinary  steelwork, 

and  Z  =  the  section  modulus,  or  =  — 

Y 

Where    I  =  the  total  moment  of  inertia  of  the  structure, 
and  Y  ==  half  the  depth  of  the  section. 

It  must  here  be  borne  in  mind  that  we  are  dealing  with  a  cantilever  composed 
of  the  structure  as  a  whole,  and  not  with  an  isolated  column.  Therefore,  in  arriving 
at  the  value  for  Z — 

.  •  * 

Y  =  half  the  total  diameter  of  the  holder  = 

2 

The  moment  of  inertia  I  can  be  found  by  the  summation  of  the  elements,  using 
the  ordinary  formula. 

Ix=Io+AD2 
Where    Ix  =  the  moment  of  inertia  of  each  element  about  the  true  neutral  axis 

of  the  section. 

10  =  the  moment  of  inertia  of  each  element  about  its  own  neutral  axis. 
A  =  the  area  of  the  element. 
D  =  the  distance  of  its  neutral  axis  from  the  true  neutral  axis. 

This  formula  is,  however,  somewhat  tedious  ;  and,  although  not  strictly  accurate, 
Eankine's  formula  is  very  much  more  easily  handled. 
The  formula  says  : — 

Z  =  0-25  NAD. 
Where  N  =  number  of  the  columns. 

A  =  cross- sectional  area  of  each  column  in  square  inches. 
D  =  diameter  of  holder  in  feet.      * 

Then,  having  found  the  value  of  Z  it.  is  possible  to  equate  this  to  the  bending 
moment  in  the  ordinary  way  : — 

Bending  moment  =  /  max  Z. 


THE    STORAGE   OF   GAS       .  431 

(It  must  be  noticed  that  the  wind  pressure  P  was  taken  in  Ibs.,  and  the  allowable 
stress  /max  is  in  tons.     The  two  must  therefore  be  reduced  to  equivalent  units.) 
From  above  : — 

8L2D+D     =6X  2240x0-25 NAD. 

o 

D3 
8L2D  + 

A  3 

or  A  = 


6  X  2240  X  0-25  N  D 
24L2  +  D2 


10,080  N 

,  .       24L2  +  D2 
'  10,000  N 

The  area  A  given  by  this  formula  is  the  cross-section  of  each  column  necessary 
to  prevent  failure  of  the  structure  as  a  whole. 

Bending  moment  on  one  bay  only. 

Consider  the  standard  as  a  beam  supported  at  both  ends  and  uniformly  loaded. 
Then  if— 

B  =  the  pitch  of  the  columns  in  feet. 

L  =    the  total  length  of  each  column.     , 

ivlz 
The  bending  moment  =     —  ,  where  w=  the  load  per  foot  run.     Working  on 

8 

the  assumptions  of  Cripps,  it  is  customary  to  consider  the  wind  pressure  equal  to  10  Ibs. 
per  square  foot,  which  is  assumed  as  acting  upon  a  length  of  standard  equal  to  three- 
quarters  of  the  depth  of  the  holder.  In  the  above  formula,  therefore,  we  have, 

3 

w  =  10  Ibs.  per  sq.  foot,  and  1=  —  L. 

4 


.'.  Bending  moment  (B6) 

10  X  B  X 


tons-feet. 


8  X  2240 

BL2 

=  (approximately)  

y     270 

The  bending  moment  (B6)  on  a  single  bay  is,  therefore,  equal  to — 

BL2. 

inch- tons 

270 

where  B  =  the  width  in  feet  of  one  bay,  i.e.  distance  from  column  to  co  lumn 

and  L  =  height  of  standard  as  before. 

(This  conclusion  appertains  only  to  those  holders  in  which  the  guide-framing  is 
carried  the  whole  way  up.) 

\  =  /  max   2 

T> 

or  Z  (the  section  modulus)  =      b    • 


432  MODERN   GASWORKS   PRACTICE 

Knowing  Z,  the  required  area  of  the  section  of  the  column  can  be  found  from 
the  following  approximate  formula  :  — 

Z=2Ay 
Where  A  =  the  area  of  each  flange  of  the  column. 

y  =  half  the  depth  of  the  cross-section  of  the  column. 

Z 

or,  A  = 

2y 
(It  will  be  noticed  that  this  gives  the  cross-  sectional  area  at  the  base,  i.e.  where 

the  greatest  stresses  have  to  be  withstood.     The  cross-sectional  area  may,  of  course, 
be  reduced  towards  the  top.) 

In  designing  a  column  the  total  area  required  must  be  taken  (i.e.  formulae  A  -(-  B). 

rm,  /24L2+D2  BL2\ 

The  total  area  =(  -  —  )  • 

V  10,000  N        3240y' 

(Note.  —  The  value  for  /  has  been  taken  as  6  tons  per  square  inch.  Cripps,  in 
order  to  allow  a  margin  owing  to  the  fact  that  the  standard  is  acting  as  a  column 
takes  a  value  of  4  tons  per  square  inch.) 

The  method  of  calculation  will  be  readily  understood  by  the  consideration  of  a 
simple  example. 

Take  a  holder  of  such  design  as  that  seen  in  Fig.  287,  having  a  capacity  of  about 
750,000  cubic  feet,  Let  the  diameter  of  the  bottom  lift  be  110  feet,  and  the  total 
height  of  the  bell  (which  is  the  same  as  the  effective  height  of  the  standards)  80  feet. 
The  standards  will  be  conveniently  spaced  at  a  pitch  of  about  16  feet  ;  or,  as  the 
tank  circle  will  measure  approximately  352  feet,  it  can  be  assumed  that  the  standards 
will  be  22  in  number. 

The  total  area  required  for  each  flange  at  the  base  of  the  standards 

=  24L2D2         BL2 
iO,COON      324cV 

In  the  example  under  consideration  :— 

L=    80  feet 

D=110     „ 

N=    22  .  „ 

B=     16     „ 

y  =  half  depth  of  cross-  section  in.  inches. 

therefore,  m=(&  X  *>  X  80)  +  (110  X  110)       16  X  80  X  80N 
V  10.CCO  X  22  3240  X  y    / 

-6 

y 

18 
Assuming  a  depth  of  18  inches  for  the  cross-section,,  y  =  —  =  9  therefore  area 

Zi 

of  each  flange  =  0-75  -|-  -      —  =  4-26  sq.  inches. 

or  total  area  of  flanges  =8-52  sq.  inches. 


A  7-    i  31-60 

=0-7o 


THE   STORAGE   OF   GAS 


433 


Part  Plan 


Crown  Rest  Pruning 


FIG.  287. — DETAIL  OP  |-MILLION  CUBIC  FEET  GASHOLDER. 

Considering  a  number  of  possible  standard  sizes  of  R.S.J.  the  following  com- 
parison may  be  made  : — 


Weight 

Theoretical  Area 

Size  of  Joist. 

Ibs.  per 

Registered 

Area  Given 

Foot. 

(Both  flanges). 

Inches 

Square  inches 

Square  inches. 

A 

18  by  6 

55 

8-52 

8-44 

1  per  cent,  deficient 

B 

18    „    7 

75 

8-52 

13-5 

excessive 

C 

16    „    6 

62 

94 

10-36 

slight  excess 

D 

15    „    6 

59 

9-92    ' 

10-73 

slight  excess 

E 

15    „    5 

42 

9-92 

6-60 

deficient 

P  F 


434  MODERN   GASWORKS   PRACTICE 

Choice  should  fall  on  the  lightest  section  which  fulfils  the  required  conditions 
as  to  stability.  Section  A  would,  therefore,  be  decided  upon,  for  the  very  slight 
deficiency  would  be  more  than  compensated  for  by  the  metal  in  the  web.  Some 
designers  might  not  care  about  a  section  so  deep  as  18  inches  for  a  holder  of  this 
size,  and  if  such  is  the  case,  that  under  heading  D,  though  slightly  heavier,  might  be 
conveniently  employed. 

It  should  be  mentioned  that  with  a  rolled  standard  of  this  description  some 
engineers  base  the  required  flange  area  on  the  figure  given  by  the  formula  relating 
to  the  bending  moment  on  the  single  bay  only,  delegating  the  remainder  (i.e.  the 
area  required  to  resist  the  capsizing  of  the  holder  as  a  whole)  to  the  web  of  the 
section.  It  is  necessary  to  emphasize,  however,  that  when  a  composite  section  of  the 
lattice-braced  type  is  adopted,  no  reliance  must  be  placed  in  the  web.  For  this 
reason,  and  also  owing  to  the  fact  that  a  maximum  stress  of  6  tons  per  square  inch 
has  been  taken,  the  author  prefers  to  deal  with  all  sections  in  the  manner  indicated 
above,  so  that  when  the  web  is  of  assistance  a  small  increase  is  obtained  in  the  gross 
factor  of  safety. 

TYPES   OF   STANDARDS 

The  ultimate  design  of  the  standards  must  primarily  be  influenced  by  the  calcu- 
lation for  area  as  shown  above.  Keeping  this  figure  in  view  and  bearing  in  mind 
generally  accepted  working  precedents,  it  is  possible  to  evolve  a  section  combining 
a  minimum  of  metal  with  a  maximum  of  stability.  For  instance,  the  metal  compos- 
ing the  flanges  may  (within  certain  limits)  be  reduced  in  proportion  to  the  increase 
in  depth  of  the  section  ;  in  other  words,  the  \veight  per  foot  run  may  be  decreased  as 
the  depth  becomes  greater.  So  far  as  the  plain  H  joist  is  concerned  this  possesses 
the  disadvantage  that  it  cannot  be  reduced  in  cross-section  towards  the  top  of  the 
columns,  thus  considerable  wastage  of  metal  occurs.  In  spite  of  this,  however,  a 
joist  will  be  found  the  most  economical  section  for  holders  up  to  about  f  million 
cubic  feet  capacity,  owing  to  the  comparatively  small  amount  of  labour  involved, 
and  in  contrast  to  the  expenditure  under  this  item  in  connexion  with  standards 
of  the  built-up  description.  Also  the  plain  girder  will  weather  better  and  offers  less 
chance  of  deterioration. 

So  far  as  the  old-fashioned  cast-iron  columns  are  concerned  it  may  be  noted 
that  gasholders  designed  on  these  lines  cannot  be  treated  as  a  braced  cantilever, 
as  is  the  case  with  the  modern  structure.  In  the  old  pattern  each  standard  forms 
a  cantilever  in  itself,  and  although  horizontal  girders,  and  in  some  instances,  light 
diagonal  ties,  connect  the  columns  together,  it  cannot  be  assumed  that  the  framework 
is  of  such  elasticity  as  to  distribute  the  loading  throughout  the  whole.  Being  of  the 
rigid  type  each  column  takes  the  loading  in  accordance  with  the  direction  in  which 
this  may  be  imposed,  and  rigidity  is  obtained  by  employing  a  superabundance  of 
dead  weight.  Fig.  288  shows  the  elevation  of  a  number  of  forms  of  gasholder 
columns,  both  steel  and  cast  iron.  The  cast-iron  designs  with  pulleys  for  the  chains 
of  counterbalance  weights  are  now  out  of  date. 


THE   STORAGE   OF  GAS 


435 


FIG.  288.— VARIOUS  FORMS  OF  GASHOLDER  STANDARDS. 


436 


MODERN   GASWORKS   PRACTICE 


DETERMINATION  OF  MAXIMUM  SHEAR 

Consider  a  braced  cantilever  as  in  Fig.  289. 
Bending  moment  =  WL,  and  this  is  resisted  by  R<£. 
(taking  moments  about  o) 


WL 

T' 


or  R  (which  is  horizontal  shearing  force  at  flange)  — 


or 


Bending  moment 

,  horizontal  shearing  force  =  — -^— — — 

Depth  of  girder 


W  Tons      W  Tons      W.  Tons      W  Tons 


The  section  we  have  to  consider  is  a  braced  cantilever  of  cylindrical  form,  i.e. 
with  no  actual  top  and  bottom  flanges.     Now  the  radius  of  gyration  of  a  hollow 

cylinder  about  a  pole  passing 
through  its  centre  is  0-707  D.  Sir 
Benjamin  Baker  considered,  there- 
fore, that  if  the  guide-framing  was 
considered  as  an  ordinary  two- 
flanged  girder  the  two  imaginary 
flanges  might  be  taken  as  occurring 
at  the  radius  of  gyration.  F.  S. 
Cripps,  however,  whose  conclusions 
on  matters  relating  to  holders  are 
accepted  as  final,  states  that,  taking 
all  things  into  consideration,  the 
depth  of  the  imaginary  girder  may 


D.F 


FIG.  289. 


be  considered  as  f  of  the  diameter 
of  the  cylinder,  i.e.  0-75  of  the 
diameter  of  the  holder,  i.e.  |D. 

Then  we  have  an  assumption  such  as  that  shown  in  Fig.  289,  the  depth  of  our  girder 

being  |D. 

Bending  moment 

It  has  been  shown  above  that  horizontal  shear  =  —  T—  :  -- 

Depth  of  girder 

But  it  has  already  been  shown  that  in  the  case  of  the  holder  framing  (see  page  430) 
the  total  bending  moment  is  equal  to  :  — 


-     -^2240  ton-inches, 
and  the  depth  of  the  girder  =  |D. 


.'.  Total  horizontal  shearing  force 


+  2240 


|D 


THE   STORAGE   OF   GAS 


437 


It  will  be  noticed  that  the  plane  of  the  shearing  force  cuts  the  framing  in  two 
points  (such  as  0  and  P),  consequently  the  shear  on  each  of  the  horizontal  planes 
will  be  half  the  total  shear,  or — 


24L2-f-D2 
10,080 


as — 


Cripps  points  out  that  sufficient  accuracy  will  be  obtained  by  taking  this  formula 

24L2+D2  , 

Horizontal  shear  = tons. 

10,000 

(It  will  be  noticed  that  the  shear  is  spoken  of  as  horizontal,  for  the  reason  that  we  are 
now    considering    a    horizontal    cantilever    as 
shown  in  Fig.  289.     In  the  case  of  the  gas- 
holder the  cantilever  is  in  a  vertical  position, 
therefore  the  shear  is  vertical  shear.) 

So  far  as  computing  the  effect  of  the 
shearing- stress  is  concerned,  Cripps  has  shown 
that  although  the  loading  on  the  standards  is 
in  reality  concentrated  at  each  roller  contact,  it 
may  be  considered  as  a  distributed  load,  for 
the  stiffness  of  the  standards  converts  the 
forces  given  out  opposite  the  rollers  into  a  distributed  load  so  far  as  the  struts  and 
ties  are  concerned. 


FIG.  290. 


THE   STRESSES   IN  A   BRACED   CANTILEVER 

The  method  of  computing  the  stresses  in  the  struts  and  ties  of  the  guide-  framing 
will  readily  be  followed  by  considering  an  ordinary  braced  cantilever  (Fig.  289) 
and    the    reciprocal     stress    diagram    for    the    same.       The 
equally  distributed  load  will  be  apportioned  amongst  each  of 
the  nodes,  the  loads  AB,  BC   and   CD,  being  equal  (W  tons) 

If,  however,  we  assume  that 


1. 

1  ° 

b 
§ 

X 

C 

A 

X 

X 

F      «„, 


W 

whilst  the  end  node  carries    — 

2 


s 


each  node  carries  an  equal  weight  (not  a  strictly  accurate 
assumption,  but  nevertheless  approved  by  Cripps)  it  is  easily 
seen  from  the  reciprocal  diagram  that  the  stress  in  the 
diagonal  ties  and  vertical  struts  increases  from  the  end  to- 
wards the  abutment  in  the  proportion  1,  2,  3,  4.  Therefore, 
if  we  have  the  total  horizontal  shear  it  is  possible  to  com- 
pute the  stress  in  the  struts  and  ties.  For  instance,  if 
the  total  shear  resolved  in  the  direction  of  the  ties,  and  Ss  is  the  total 


438  MODERN   GASWORKS   PRACTICE 

shear  resolved  in  the  direction  of  the  struts — then,    if   we   have   four   panels 

1+2+3+4=10 

4 

.'.  Tension  in  tie  nearest  abutment  :=        of  S, 

JO 

„    tie  in  2nd  panel  =  ^    „     „ 

„    tie  in  3rd      „  =         „     „ 

„    tie  in  4th      „  _ 

Similarly  (see  reciprocal  diagram,  Fig.  289), 

4 

Compression  in  strut  nearest  abutment  =        of  S, 

10 

„       „       in  2nd  panel          =  --    „     „ 
3rd  —  2 

J)  5J  JJ  53    "•'•'-I  )}  1A         "  " 

5>        •  j?       ?j         J3  4tn       ,,  —  —    ,,     ,, 

In  the  example  already  considered  the  height  of  the  columns  was  80  feet,  the 
distance  apart  16  feet,  and  it  may  be  assumed  that  there  would  be  four  equal  panels 
as  in  Fig.  291. 

The  length  of  diagonals  AC  and  BD  is  readily  calculated.     Then — 

24  L2   I  D2 

Maximum  vertical  shear= —  tons  =  16-57  tons. 

10,CCO 

Resolving  this  in  direction  of  struts  we  get — 

1  £. 

Total  compression  in  struts  =  16-57  X  — =  13-24  tons. 

4 
Compression  in  bottom  strut  = —  X  13-24=    5-29  tons. 

Resolving  16-57  tons  in  direction  of  ties,  we  get — 

25-6 

Total  tension  in  ties=  16-57  X =  21-2  tons. 

20 
4 
Tension  in  bottom  ties=  —  X  21-2  =  8-5  tons. 

The  above  calculations  give  the  maximum  compressive  and  tensile  stresses 
occurring  in  struts  and  ties,  the  members  in  the  lowest  panel  being  subjected  to  this 
loading.  From  previous  statements  it  will  be  seen  that  the  stresses  in  the  individual 
struts  and  ties  decrease  towards  the  top  of  the  framework ;  hence,  theoretically,  the 
section  of  these  members  may  be  reduced  in  proportion.  In  practice,  however,  it 


THE   STORAGE   OF   GAS  439 

is  frequently  the  custom  to  allow  for  all  struts  to  be  of  similar  section,  although  in 
the  case  of  the  larger  holders  some  reduction  is  admissible  and  conducive  to  economy. 
This  particularly  applies  to  holders  having  built  up  struts  such  as  the  lattice  or  open- 
box  type.  It  must  be  borne  in  mind,  however,  that  there  is  some  tendency  to 
deformation  due  to  torsion,  and  this  torsional  force  is  a  maximum  at  the  top  of  the 
framing.  Hence,  too  liberal  a  reduction  in  the  section  of  the  upper  struts  should 
not  be  permitted. 

THE  DESIGN  OF   STRUTS 

Struts  are  best  designed  by  trial  and  effect  methods.  That  is  to  say,  an  engineer 
acquainted  with  the  practical  construction  of  holders  will  decide  upon  what  he 
considers  to  be  a  reasonable  section,  and  will  then  prove  the  stability  of  his  section 
by  ordinary  theoretical  methods.  For  this  purpose  the  safe  load  which  the  strut  is 
capable  of  withstanding  may  be  calculated  from  the  following  modification  of  the 
"  straight  line  "  formula  which  the  author  suggests  as  being  the  most  adaptable  for 
the  purpose  : — 

Safe  load  =6  fl — G053_j  X  area  of  section.  ,  ' 

Where,  L  —  length  of  strut  in  inches 
K  =  least  radius  of  gyration. 

Then,  the  section  must  be  such  that  the  safe  load  given  is  not  less  than  the 
compressive  stress  in  the  member  calculated  as  shown  above. 

To  return  to  the  example  in  question,  the  maximum  stress  in  the  bottom  strut 
is  5-29  tons.  For  a  holder  of  this  size  the  struts  would  be  most  economically 
composed  of  ordinary  R.S.  J.  The  probable  section  required  would  be  10"  by  5"  by 
30  Ibs.  per  foot.  Applying  the  test  formula  to  this,  we  get : — 

Safe  load=    6^1  -  -0053—)  X  area 

/  1  fi  y  1 9\ 

=    6(  1--0053X  )  X  8-82 

V  1-05    / 

:    6  (1--9699)  X  8-82 
=  52-92  X  -0301 
=    6-76  tons. 

The  section  is  therefore  amply  strong  for  the  purpose. 

(Note. — The  value  of  K  for  above  may  be  readily  obtained  from  one  of  the  many 
sections  tables  published  by  the  steel  manufacturers,  or  it  may  be  calculated  from 

the  principle  that  K  =A/    -,  where  I  is  the  least  moment  of  inertia  of  the  section.) 

THE  DESIGN  OF  TIES 

The  design  of  the  tie-bars  which,  with  few  exceptions,  consist  of  plain  round 
mild  steel  rods  is  simple.  If  the  load  on  the  tie  is  known  then  the  following  formula 
gives  the  required  diameter  : — 

T..  •     •     i  /Load  in  tons 

Diameter  in  inches  =\/ 

V  4-71 


440 


MODERN   GASWORKS   PRACTICE 


In  the  example  in  question  the  maximum  tension  was  found  to  be  8-5  tons,  therefore — 


diameter  of  tie  bar 


/  8-5 
=V  r~ 


Pull  of  Plates 


•5 

_4-71 

=Vf-8=l-34  inches, 
or,  say,  a  1|  inch  or  1£  inch  bar. 

Round  bars  are  to  be  preferred  to  other  sections,  such  as  flats,  tees  or  channels, 
in  that  they  are  more  simply  connected  to  the  standards  and  are  more  adaptable 
for  tension  gear.  Care  should  be  taken,  however,  to  ensure  that  the  rods  are  thickened 
at  the  screwed  end,  so  that  there  is  no  loss  in  strength  when  the  screw  is  cut.  When 
connecting  eyes  are  employed  they  must  be  of  such  design  as  to  be  of  equal  strength 
to  the  bar.  The  attachment  of  the  eye  to  the  standard  should  be  such  that  the 
connecting  pin  is  in  double  shear. 

It  will,  of  course,  be  understood  that  of  the  two  diagonal  ties  in  each  panel  only 
one  is  under  stress  at  a  time. 

THE  HOLDER  BELL 

In  the  design  of  the  holder  bell,  particular  consideration  must  be  given  to  the 
top  curb  (where  side  sheets  and  top  sheets  meet),  the  ring  curb  at  the  base  of  the  top 
lift,  and  the  curbs  at  the  upper  and  lower  edges  of  succeeding  lifts. 

The  top  curb,  owing  to  the  gas  pressure 
on  the  dome,  is  by  far  the  most  highly 
stressed.  The  forces  acting  on  it  are  shown 
in  Fig.  292.  They  produce,  as  is  seen,  a  com- 
pound stressing  which  tends  either — 

(a)  To  tear  the  top  bodily  away  at  the 
junction  of  side  and  dome  plates. 

(6)  To  buckle  the  curb,  side  plates  or 
dome  plates. 

The  function  of  the  top  curb  is,  therefore, 
to  resist  these  tendencies,  whilst  an  additional 
safeguard  is  provided  against  the  blowing-in 
of  the  side  sheets  by  interposing  vertical 
stiffeners  at  intervals  around  the  cylinder. 
The  resultant  pressure  of  the  gas  on  the  in- 
terior of  the  dome,  and  the  weight  of  the 
plates  composing  the  dome,  will  be  such  as  to 
produce  a  pull  in  the  plates,  the  direction  of 
which  pull  will  be  at  a  tangent  to  the  point  under  consideration.  So  far  as  the 
plates  forming  the  sides  are  concerned,  the  effect  of  the  internal  gas  pressure  is  to 
produce  a  slight  ring  tension,  but  the  plates  are  of  necessity  more  than  strong 
enough  to  cope  with  this.  The  ring  stress  is  transmitted  to  the  curbs  by  the 
vertical  stiffeners,  and  in  this  way  assists  in  counteracting  the  compression  in  the 
curbs.  If  buckling  or  distortion  of  the  curb  took  place  the  ring  tension  would  have 


Weight  of 
Side  Sheeting 


Total  Wind 
FIG.  292. 


THE   STORAGE   OF   GAS 


441 


a  tendency  to  right  the  whole  to  its  circular  form,  but  the  effect  would  be  almost 
inappreciable. 

By  a  consideration  of  the  main  forces,  it  may  be  shown  from  the  polygon  of 


FIG.  293. — TOP  CURBS  FOB  GASHOLDERS. 


forces  (Fig.  292)  that  the  resultant  acts  in  such  a  direction  as  to  induce  a  compressive 
stress  in  the  curb.  The  direction  of  the  resultant  will,  in  fact,  be  horizontal  and  in 
alignment  with  the  direction  of  the  wind.  In  the  diagram  of  forces  (Fig.  292)  the 


FIG.  294. — COMMON  DESIGNS  FOR  BOTTOM  CURBS. 

resultant  has  been  slightly  tilted  in  order  to  show  the  conditions  more  clearly.  Failure 
of  the  curb  will  be  due,  as  may  be  seen,  to  an  excessive  compressive  ring  stress.  In 
practice,  however,  the  chief  danger  of  buckling  lies,  not  so  much  in  the  stresses 
produced  by  wind  and  top  pull,  but  from  the  possibility  of  the  bell  tilting  during 
its  movement  on  the  guide  stanchions.  In  this  direction  a  heavy  drift  of  snow 
might  give  rise  to  danger. 


442  MODERN   GASWORKS   PRACTICE 

For  the  purpose  of  withstanding  any  buckling  effort  which  might  occur,  the 
dome  curb  in  holders  of  any  size  should  preferably  be  designed  on  the  girder  principle, 
or  be  provided  with  suitable  gussets.  Various  forms  of  gasholder  curbs  are  shown 
in  Fig.  293.  Cripps  has  pointed  out  that  if  these  curbs  are  of  sufficient  strength  to 
resist  the  compressive  stress,  then  there  will  be  little  likelihood  of  buckling.  Common 
designs  for  bottom  curbs,  that  is  the  lower  curb  of  the  bottom  lift,  are  shown  in 
Fig.  294. 

COMPRESSION   IN   THE    TOP  CURB 

The  compressive  stress  in  the  top  curb  and  hence  its  necessary  dimensions  may 
be  calculated  as  follows  : — 

Let  D  be  the  diameter  of  the  top  lift,  in  feet. 

,,    R    ,,     ,,      rise  ,,     ,,    dome,  in  feet. 

,,    P    ,,     ,,     effective  pressure  thrown  by  the  holder  in  Ibs.  per  square  foot. 
As  regards  pressure  it  will  be  seen  that  if  the  total  weight  of  the  holder  bell 

W  Ibs 

is  W  Ibs.,  then  the  nominal  pressure  thrown  would  be —  — - .       It  is  neces- 

area  of  bell 

sary  to  consider,  however,  the  upward  pressure  of  the  gas  on  the  do^ne  sheeting,  which 
actually  detracts  from  the  total  weight  of  the  dome. 

Thus,  if  iv  =  the  weight  of  the  top  sheeting  in  Ibs.  per  square  foot, 

and  h  =  the  gross  pressure  thrown  by  the  holder  in  Ibs.  per  square  foot, 
then  the  effective  pressure  will  be  : — 
(h-w)X  area  of  bell  =     -7854  D2  (h  -  w)  =  P. 
The  net  upward  thrust  on  the  dome  due  to  the  gas 
will  then  be  equal  to  -7854  D2  (h  —w),  that  is  the  effective 
pressure  P.  Then,  referring  to  Fig.  295,  it  will  be  seen  that 
the  resultant  vertical  thrust  is  kept  in  equilibrium  by  the 
tangential  pull  at  the  circumference  acting  at  an  inclina- 
tion DF  or  EF.      In  the  triangle  of  forces  FDO,  if  OF 
represents  the   net  upward  thrust  of  the  gas,  then  DF 
represents  in  magnitude  and  direction  the  tangential  pull 


FIG.  295.  in  the  plates. 

OF=P 
FO  FO 


and  DF  = 


sin.  FDO      sin.  a 


m,       ,  **  i    '  11   T         P 

Therefore,  tangential  pull,  T  =  - — 


sin.  a  sm.a 

Or,  T,  per  foot  length  of  circumference  =  -       — X  — 

sm.a  irD 

J)(h—w]  f    .          , 

i.e.  T  =  — -  per  toot  of  circumference. 

4  sin.  a 

DP 

But  (h  —  w)  =  effective  pressure  =  P    .'.  T  =  — - 

4  sin. a 


THE    STORAGE    OF   GAS  443 

This  result  is  approximate,  but  any  error  is  on  the  safe  side.  If  the  above 
expression  gives  the  pull  per  foot  of  circumference  then  the  total  pull  over  the  whole 
diameter — 


and  this  thrust  is  taken  by  the  two  sections  of  the  curb  diametrically  opposite. 
Therefore,  thrust  on  each  section — 

,  /   DP  \_     D2P 

X  -L'  )  — 


\4sin.  a         /      8  sin.  a 
WEIGHT  OF  THE  SIDE  SHEETS. 

This  may  be  calculated  by  taking  out  the  weight  of  the  side  sheeting,  curbs, 
guide  rollers,  etc.,  from  the  specification  or,  more  readily,  from  a  consideration  of 
the  above  formula.  The  effective  pressure  thrown  by  the  holder  must  necessarily  be 
derived  from  the  weight  of  the  side  sheeting,  for  owing  to  the  upward  thrust  of  the 
gas  upon  the  dome  the  weight  of  this  portion  is  ineffective.  Considering  Fig.  295,  it 
will  be  seen,  then,  that  the  weight  of  the  side  sheets  is  represented  by  the  vertical 
component  of  the  tangential  pull  T  ;  moreover,  the  resultant  of  the  two  forces  T 
and  W  must  be  horizontal,  otherwise  the  holder  bell  would  not  be  in  equilibrium,, 
but  would  tend  to  be  always  moving  upwards  or  downwards  in  its  framing. 

The  resultant  of  T  and  W  is,  therefore,  represented  by  the  line  DO  (Fig.  295).. 
.'.  Resultant  =  T  cos.a 

D2P  D2P 

X  cos.  a  = X  cotan.  a 


8  sin.  a  8 

The  angle  a  may  be  readily  found  as  follows  : — 

D2  —  4R2 

Cos.  a  =  -  -  where  D  =  diameter  of  holder  in  feet, 

D2  -|-4R2 

and  R  =  rise  of  dome  in  feet. 

INTERNAL  PRESSURE  OF  GAS  ON  SIDES 

Cripps'  method  of  calculating  the  effects  of  this  force  is  to  consider  the  ring: 
tension  in  the  side  sheets,  and  to  allow  a  definite  proportion  of  this  as  transmitted 
to  the  curbs.  Thus  ring  tension — 

— —  where  d  =  depth  of  lift  in  feet. 

2 

Then  y1^  of  the  above  is  taken  for  holders  having  vertical  stays  attached  through- 
out their  length,  and  ^s  for  stays  attached  at  top  and  bottom  only.  The  effect  of 
the  internal  gas  pressure  is  to  counteract  in  some  degree  the  external  wind  pressure 
and  buckling  effect.  The  extent  to  which  this  effect  is  felt  is,  at  all  events,  an  uncertain 
factor ;  and,  in  the  light  of  practical  observations,  the  author  considers  that  it  is 
quite  reasonable  to  allow  for  it  by  deducting  55  per  cent,  from  the  usual  figure 
taken  for  maximum  wind  pressure  on  a  cylindrical  surface  ;  that  is  to  say,  to  assume 
external  effective  wind  pressure  at  12  Ibs.  instead  of  26  Ibs.  per  square  foot.  This,  of 
course,  applies  to  those  cases  in  which  the  vertical  stays  are  attached  throughout 
their  length.  Such  an  allowance  would  be  representative  of  the  effect  in  the  majority 


444  MODERN   GASWORKS   PRACTICE 

of  holders  now  erected,  and  in  the  case  of  the  very  large  holders  any  slight  error  would 
be  on  the  right  side. 

Objection  might  be  raised  to  this  method  owing  to  the  fact  that  the  gas  pressure, 
the  magnitude  of  which  is  easily  computed,  is  taken  as  constant  in  all  holders.  But  as 
the  whole  treatment  must  necessarily  be  one  of  some  conjecture  the  author  considers 
that  his  assumption,  owing  to  its  simplification  of  formulae,  is  perfectly  justifiable. 

Effective  wind  pressure,  therefore, 

=  D  X  d  X  12  Ibs.  per  square  foot. 

But  this  is  distributed  to  both  upper  and  lower  curbs  of  the  lift  and  is  also 
withstood  by  the  two  diametrically  opposite  sections  of  the  curb.  Accordingly, 
the  total  force  on  any  section  of  the  curb, 

=  -X  D  X  dX  12  =  3Dd. 
4 

By  a  summation  of  the  above  force  and  the  resultant  of  the  tangential  and 
vertical  pulls,  which  act  parallel  with  the  wind,  the  total  compressive  force  on  the 
curb  may  be  readily  calculated. 

COMPRESSIVE  FORCE  IN  TOP  CURB 

D2Pcotana    . 
=  -  +  o  Da. 

8 

Where  D  =  Diameter  of  holder  in  feet. 

P  =  Effective  pressure  in  Ibs.  per  square  foot. 

a  =  Angle  made  by  tangent  with  chord  at  base  of  the  dome  or,  the 
angle  a  may  be  found  from  the  following.  (Note  the  formulae 
gives  cos.  a  and  not  cotan.  a  direct.) 

D2  —  4  R2 

Cos.  a=  —  where  R  —  rise  of  dome  in  feet. 

R2 


d  =  Depth  of  top  lift  in  feet. 

In  the  event  of  the  holder  being  designed  with  vertical  stays  attached  at  top 
and  bottom  only,  substitute  5Dd  for  the  expression  3Dd  above. 

Having  obtained  the  total  compressive  force  it  is  merely  necessary  to  design  a 
curb  of  sufficient  cross-  sectional  area  to  safely  withstand  this.  A  stress  of  6  tons 
per  square  inch  should  not  be  exceeded.  In  calculating  the  cross-  sectional  area  it 
.should  be  remembered  that  the  two  outer  crown  rows  and  the  two  top  side  rows  of 
the  sheeting  may  be  included  in  the  effective  area.  These  plates  should  be  butted, 
when  the  full  cross-  sectional  area  may  be  considered  effective,  but  if  lapped  the 
sh  earing  strength  of  the  rivets  only  should  be  considered. 

CUPS   AND   GRIPS 

The  proportions  of  cups  and  grips  for  telescopic  holders  have  already  been  dealt 
with  (page  426).  There  are  two  standard  types,  namely  the  semi-circular  cup  and 
grip  as  seen  in  Fig.  296,  and  that  composed  of  the  square  channel  section  (Fig.  297). 
The  channel  type  is  strongly  to  be  preferred.  It  is  simply  constructed,  while  it 


THE   STORAGE   OF   GAS 


445 


obviates  the  objectionable  initial  stress- 
ing which  is  set  up  in  the  semi-circular 
grip  when  the  plate  is  bent  to  shape. 
Moreover,  if  one  portion  is  not  in  per- 
fect alignment  with  its  counterpart,  a 
grinding  action  will  be  set  up  when 
the  two  come  together.  This  will  be 
particularly  severe  when  there  is  some 
slight  constructional  defect,  such  as  the 
grip  being  slightly  larger  than  the  cup, 
or  if  the  two  are  not  set  to  an  exact 
circle.  If  the  grip  is  slightly  large  the 
cup  will  not  engage  centrally,  with  the 
result  that  the  grip  is  slightly  tilted 
and  the  guide  rollers  are,  in  turn, 
thrust  hard  over  against  the  columns. 
The  effect  will  be  noticed  by  a  con- 
sideration of  Fig.  298.  The  tendency 
can,  of  course,  be  minimized  by  addi- 
tional guide  rollers  on  the  grip  running 
on  guides  attached  to  the  inner  lift. 


FIQ.  297. — SQUARE  CUP  AND  GRIP. 


FIG.  296. — SEMI-CIRCULAR  CUP  AND  GRIP. 

When  properly  constructed,  the  grip  with 
the  weight  it  carries  should  act  as  a  steadi- 
ment  to  the  inner  lift,  and  counteract  any 
tendency  towards  tilting. 

When  designing  the  cup  and  grip, 
sufficient  width  should  be  allowed  so  that 
riveting  may  be  carried  out  with  ease. 
The  minimum  width  should  be  8  inches. 
The  cup  sides  and  cup  rows  on  the  bell  must 
be  stouter  than  the  normal  side  sheeting, 
and  a  beading,  to  increase  rigidity,  should 
be  run  all  round  at  the  base  of  the  cup 
side.  The  stouter  cup  sheets  will  prove 
effective  in  meeting  any  corrosion  due  to 
the  changing  level  of  the  water  in  the  lute. 
In  addition,  they  avoid  the  undesirable 
practice  of  riveting  very  thin  sheets  to  the 
thick  section  of  the  cup  or  curb.  The 
thickening  up  of  these  plates  enables  the 
reduction  to  be  effected  in  two  steps.  For 
the  cup  rows  and  cup  sides  £•  inch  sheeting 


446 


MODERN   GASWORKS   PRACTICE 


FIG.  298. 


is  common,  while  the  beading,  which  may  be  either  moulded  or  flat,  varies  from  f  inch 
to  |  inch  thick  ;  but  everything,  of  course,  depends  upon  the  size  of  the  holder. 
•  The  crown  sheeting  of  gasholders  varies  from  14  gauge  to  10  gauge  in  thickness 
(i  e.  -fa  inch  to  £  inch),  depending  entirely  upon  the  size  of  the  holder  ;  curb 
rows  being,  of  course,  thicker  (  \  inch  to  f  inch  in  medium  sized  holders,  and  so  much 
as  |  inch  in  large  holders).  As  regards  side  sheeting,  this  varies  from  12  gauge  to 
10  gauge  in  thickness  ;  curb,  or  cup  and  grip  rows  again  being  heavier.  The  side 
sheets  of  the  top  lift  are  occasionally  thicker  (say  8  gauge)  than  those 
of  succeeding  lifts  ;  and  it  should  be  remembered  that  where  joints 
between  rolled  sections  and  plates  occur  it  is  always  advisable  to  use 
heavier  plates,  so  as  to  avoid  attaching  a  very  thin  section  to  a  thick 
one,  a  practice  generally  followed  by  imperfect  and  leaky  joints.  The 
sheets  employed  should  be  as  large  as  practicable,  for  the  jointing  is 
then  reduced  to  a  minimum  and  the  labour  of  riveting  is  lessened. 
On  the  other  hand,  smaller  plates  and,  therefore,  more  liberal  rivet- 
ing have  a  tendency  to  stiffen  up  the  whole  shell. 

The  thinner  sheets  of  the  gasholder  bell  are  usually  riveted  up 
cold  with  \  inch  rivets  at  a  pitch  of  1  inch,  or  ^  inch  rivets  at  1£ 
inch  pitch.  Curb  and  such  rows  have  stiffer  rivets  at  a  slightly 
greater  pitch,  but  all  rivets  above  \  inch  diameter  must  be  driven 
hot.  For  the  purpose  of  making  the  joints  between  the  plates 
gastight,  it  is  essential  to  insert  at  the  lap  strips  of  tape  soaked  in  red  lead. 

SUPPORT  FOR  THE   CROWN 

The  dome  of  a  gasholder,  owing  to  its  frail  construction,  requires  some  form  of 
support  when  the  holder  is  grounded  and  is  receiving  no  support  from  the  internal 
pressure  of  the  gas.  There  are  two  common  methods  of  preventing  the  crown  from 
buckling  inwards,  namely  :  — 

(a)  The  provision  of  an  internal  trussing  to  the  crown,  on  the  lines  of  the  framing 
of  an  umbrella. 

(b)  The  erection  of  a  crown  rest  in  the  tank. 
In  the  former  method  the  framing  is  affixed 

to  a  series  of  rafters  radiating  from  the  centre 
and  attached  to  the  crown  curb.  A  strong 
centre  column  is  also  provided,  and  when  the 
holder  is  grounded  this  rests  on  a  bed-plate  or 
pier  in  the  centre  of  the  tank  (Fig.  299).  For 
smaller  holders  the  crown  trussing  is  generally 
employed,  and  Cripps  says  that  it  would  be 
unwise  to  abolish  the  system  in  the  case  of 
the  smaller  crowns,  for,  owing  to  its  lightness, 
it  would  be  impossible  to  put  anything  cheaper 


>.  299.-Cnowx  TBUSSISG  FOB  HOLDER. 


into  the  tank  in  the  form  of  separate  frames.     The  amount  of  metal,  and  conse- 
quently the  cost,  increases  rapidly  as  the  holder  becomes  larger,  so  that  it  may  be 


THE   STORAGE   OF   GAS 


447 


JTH 

u 

. 

i: 

s^ 

1 

; 

* 

••/ 

FIG.  300. — DIAGRAM  OF  TELESCOPIC  HOLDER  AND  GUIDE-FRAMING. 


said  that  the  trussed  crown 
must  be  limited  to  holders 
not  having  a  greater  diam- 
eter than  about  170  feet. 
The  weight  of  the  trussing 
in  large  holders  wrould  tend 
to  distort  the  spherical 
shape  of  the  crown,  which 
the  upward  gas  pressure  is 
assisting.  The  internal 
framing  should  be  as  inde- 
pendent of  the  crown  sheet- 
ing as  possible  in  order  to 
prevent  the  possibility  of 
straining  the  seams. 

As  regards  the  crown 
rest  this  consists  of  a  series 
of  radiating  rafters  carried 
on  columns  erected  in  the 


tank  and  connected  together      Fia.  301.— HOUSED  GASHOLDER  AT  TEGEL  (BERLIN) 


WORKS. 


448 


MODERN   GASWORKS   PRACTICE 


Tee 


Rd 


FIG.  302. — DIAGRAM  OF  TELESCOPIC  SPIRAL  GUIDED  HOLDER. 


by  purlins  to  form  a  skeleton  framework  of  the  same  camber  as  the  dome.     The 

frame  is  frequently  constructed  from 
timber,  although  light  sections  of 
rolled  steel  may  be  economically  em- 
ployed. The  design  is  simple  and 
may  be  seen  in  Figs.  287  and  3C2:. 
An  important  consideration  is  that  of 
arranging  for  the  bracing  of  the 
columns,  which  are  usually  of  some 
considerable  height,  particularly  in 
the  cases  of  the  flat-bottomed  steel, 
tanks. 

A  complete  diagram   of    a    tele- 
scopic gasholder  with  guide  framing  is  given  in  Fig.  300. 

An  interesting  feature  of  some  of  the  earlier  gasholders  was  the 
housing  which  was  erected  over  and  around  them  as  a  means  of  pro- 
tection. A  notable  example  of  the  covered  gasholder  is  that  at  the 
Tegel  works  of  the  Berlin  municipality  (Fig.  301).  The  building  is  an 
architectural  work  of  brilliance,  being  3CO  feet  in  height  and  overlook- 
ing the  whole  of  the  northern  part  of  the  city.  The  capacity  of  the 
holder  is  nearly  8  million  cubic  feet,  and  the  cost  complete  with 
house  was  £107,000.  An  unusual  feature  is  the  lead-covered  oil 
storage  reservoir  in  the  middle  of  the  tank. 


FIG.  303. — CROWN  CURB  FOR 
TELESCOPIC  HOLDER. 


THE   STORAGE   OF   GAS 


449 


SPIRALLY   GUIDED   GASHOLDERS 

The  spirally  guided  gasholder,  the  proposal  of  Mr.  W.  H.  Y.  Webber  and 
the  invention  of  Mr.  W.  Gadd  (Fig.  282,  p.  423)  with  which  an  external 
guide-framing  is  wholly  unnecessary,  was  first  installed  in  this  country  in  1888. 
At  the  time  of  its  introduction  there  was  much  discussion  as  to  the  stability  of 
the  design,  and  many  engineers  pronounced  the  system  as  dangerous.  As  holders 
of  the  kind  have  now  been  in  operation  for  upwards  of  twenty-five  years,  there 
can  be  little  doubt  that  with  proper  precaution  in  design  and  supervision  during 
working  they  are  no  more  likely  to  fail  than  the  guided  types,  whilst  with  modern 
improvements  there  is  practically  no  limit,  within  reason,  to  the  dimensions  to 


FIG.  304. — DUAL  GUIDE-ROLLERS  FOR  SPIRAL  HOLDER. 

which  they  may  be  constructed.  Briefly,  the  principle  of  their  operation  is 
dependent  upon  the  introduction  of  spiral  guide  rails  affixed  to  the  holder  side, 
these  acting  in  lieu  of  the  vertical*  standards  and  bracing  of  the  more  common 
type  of  holder.  The  spiral  rails  engage  with  rollers  on  the  edge  of  the  tank  in 
such  a  manner  that  the  bell  screws  itself  up  and  down.  The  direction  of  the 
spiral  may  be  either  left-handed  or  right-handed,  or  successive  lifts  may  operate  in 
reverse  directions  as  shown  in  Fig.  302.  The  rails  on  the  outer  lift  must  be  affixed 
to  the  exterior  of  the  bell,  but  those  on  succeeding  lifts  may  be  either  interior  or 
exterior,  although  the  latter  are  invariably  employed.  The  holder  seen  in  Fig. 
302  is  of  the  four-lift  spiral  type,  operating  in  an  annular  brick  ta'nk.  The  crown 
is  untrussed,  being  supported,  when  the  bell  is  grounded,  by  a  timber  framing. 
It  will  be  noticed  that  to  the  two  lower  lifts  are  attached  twin  spiral  rails,  which 

o  G 


450 


MODERN   GASWORKS   PRACTICE 


FIG.  305. — MULTIPLE  ROLLER  CARRIAGE  FOR 
SPIRAL  HOLDER. 


are  desirable  in  all  spiral  holders  of  250  feet  diameter  and  upwards.  (As  the 
effect  of  frost  might  be  attended  by  serious  results,  it  is  frequently  the  custom  to 
instal  an  anti-freezing  apparatus  in  connection  with  the  water-lutes  of  modern 

holders.)  It  will  be  seen  that  it  is 
the  guide  rollers  which  have  to  with- 
stand the  ordinary  forces  acting  on 
the  bell,  and,  through  them,  the  forces 
are  transmitted  to  the  upper  tank 
curb.  The  curb  has,  accordingly,  to  be 
of  particularly  stout  construction,  the 
more  so  if  provision  is  made  in  the 
original  structure  for  the  insertion  of 
an  additional  (outer)  lift  at  some  later 
date,  in  which  case  the  tank  rollers 
will  have  a  considerable  overhang. 

Per  unit  of  capacity  the  spiral 
holder  is  considerably  cheaper  than 
the  guide  framed  type.  It  requires, 
however,  great  accuracy  of  fitting ; 
and,  when  composd  of  a  number  of 

lifts,  an  element  of  danger  from  "  jamming  "  or  breakage  is  introduced  by  the  numer- 
ous sliding  brackets  and  rollers.  Trouble  might  chiefly  be  expected  in  countries 
in  which  marked  variations  of  temperature  are  met  with,  for  the  bell  is  subject 
to  a  certain  amount  of  radial  contrac- 
tion and  expansion.  This  difficulty 
has  been  overcome  by  the  introduction 
of  special  compensating  carriages.  The 
bell  of  the  spiral  holder  is  of  much 
stiffer  construction  than  that  of  the 
ordinary  holder,  and  some  form  of  truss- 
ing is  usually  employed  in  the  crown. 
A  suitable  form  of  crown  curb  for  a 
holder  of  about  125  feet  diameter  work- 
ing on  this  principle  is  seen  in  Fig.  303. 
The  guide  rollers  are  either  of  the 
dual  or  multiple  type.  The  dual  type 
illustrated  in  Fig.  304  are  provided 
with  continuous  automatic  lubrica- 
tion, being  so  designed  that  the  axle 
runs  in  a  bath  of  oil  formed  in  the  bed- 
plate of  the  carriage.  The  multiple  roller  carriage,  in  which  four  instead  of  two 
rollers  are  employed,  is  shown  in  Figs.  305  and  306.  It  will  be  observed  that  the 
bolts  securing  the  carriage  are  brought  as  near  as  possible  to  their  work,  thus 
reducing  the  strain  from  leverage  upon  the  tank  and  the  carriage.  As  regards  pro- 


FIG.  306. — MULTIPLE  ROLLER  CARRIAGE. 


THE   STORAGE   OF   GAS 


451 


vision  for  any  radial  contrac- 
tion or  expansion  of  the  bell, 
this  is  usually  arranged  for  by 
fitting  a  sliding  axle  as  in  Fig. 
307.  The  oil  grooves  in  the 
axle,  and  the  special  packing 
rings  at  front  and  back  to 
prevent  the  lubrication  from 
being  lost,  will  also  be  noticed. 
The  roller  is  not  free  to  revolve 
on  the  axle,  but  fixed  to  it. 
The  space  for  expansion  is 
shown  between  the  back  of 
the  roller  and  the  front  of 
the  carriage.  A  recent  feature 
is  the  "  run  down  stop  " 
which  is  affixed  at  the  upperends  of  the  guide  rails.  At  the  inquiry 


FIG.  307. — SLIDING  AXLE  FOR  ROLLER. 


-5L 


Existing  Column  Stone 


New  Concrete  Keyed 
into  Brickwork 


H.D.  Bolt  and  Plate  fixed 
behind  Existing  Brickwork^r 


\ 


Gasholder  Shell  f 


/ 


Cast-iron  Shield  fitted  with 
Cement  to  Prevent  Corrosion 
of  H.D  Bolts  at  Water  Line 


S  Existing  Tank  Wall 


Patent  Flat  H.D.  Strap  Bolts 


-  Cast-iron  Anchor  Bolts 


FIG.  308. — SHOWING  METHOD  OF  ATTACHING  ROLLER  CARRIAGE  TO  BRICK  TANK. 


held    in 

connexion  with 
the  gasholder 
accident  at 
Ilkeston  it  was 
suggested  that 
the  outer  lift 
"  jammed  "  and 
the  inner  lift  ran 
through  and  fell 
into  the  tank, 
the  concussion 
thereby  causing 
fracture  of  the 
latter.  The  "run 
down  stop  "  pre- 
vents such  an 
occurrence,  and 
may  be  readily 
fitted  to  existing 
gasholders.  I  n 
Fig.  308  is  shown 
the  method  of 
holding  down 
the  roller  car- 
r  i  a  g  e  to  the 
upper  edge  of  a 
brick  tank.  The 


452 


MODERN   GASWORKS   PRACTICE 


method  shown  is   particularly  applicable  when  a  tank  formerly  constructed  to 
take  a  bell  guided  by  standards  is  adapted  for  the  use  of  a  spiral  holder. 

THE   NUREMBERG  HOLDER 

So  far  as  originality  is  concerned,  the  new  "  floating  roof  "  holder  (hailing  from 
Nuremberg)  demands  a  certain  amount  of  attention.  The  principle  employed 
permits  of  the  expensive  water  tank  being  dispensed  with  altogether,  although  "  gas- 


xxxxxxxxx 


Detail  of  Seal 


FIG.  309. — THE  NUREMBERG  HOLDER. 

tightness  "  is  ensured  by  the  use  of  a  water  seal  as  heretofore.  Simply  explained, 
the  holder  (Fig.  309)  consists  of  an  outer  cylindrical  shell  very  similar  in  appearance 
to  the  present  holder  bell,  but  with  the  exception  that  the  roof  is  the  only  moving 
portion.  The  contrivance  is,  in  fact,  little  more  than  a  cylindrical  tank,  the  roof  of 
which  is,  by  means  of  guide  rollers,  permitted  to  rise  or  fall  within  the  tank.  Gas 
in  the  ordinary  way  is  admitted  beneath  the  roof,  which  ascends  and  descends  in 
accordance  with  the  prevailing  pressure  in  the  interior.  The  guidance  of  the  floating 
roof  is  such  that  the  smallest  amount  of  clearance  is  permitted  between  it  and  the 
internal  periphery  of  the  cylinder.  The  means  employed  for  the  prevention  of  gas 
leakage  consists  in  pumping  water  upon  the  exterior  of  the  roof  so  that  it  runs  down 
to  the  portions  above  the  guide  rollers  and  seals  up  the  clearance  between  cylinder 
and  dome.  Some  portion  of  the  water  is,  of  course,  continually  passing  through  this 
clearance  into  the  interior  of  the  holder,  whence  it  is  removed  by  way  of  a  seal  and 
returned  to  the  suction  of  the  pump. 


THE   LIVESEY  MAN-LID 

The  man-lid  introduced  by  the  late  Sir  George  Livesey  is  a  convenient  device 
commonly  fitted  to  holders  for  facilitating  inspection  of  the  gas  inlet  and  outlet  pipes. 


THE   STORAGE   OF   GAS 


453 


In  the  ordinary  way,  if  a  simple  manhole  cover  was  employed  the  gas  between  the 
waiter  level  and  the  crown  would  be  lost. 
The  man-lid,  however,  prevents  this. 
It  consists  (Fig.  310)  of  a  circular  hood 
bolted  to  the  underside  of  the  gas- 
holder crown.  To  the  side  of  the 
hood  is  attached  a  seal  tank  with  a 
feather  plate  projecting  halfway  down 
into  it.  There  is  an  aperture  in  the 
hood,  near  the  crown,  to  allow  the 
gas  in  the  hood  to  escape  when  the 
holder  is  coming  down  on  to  the  rest 
stones.  When  the  bell  is  at  rest  the 
seal  tank  is  filled  with  water  until 
the  seal  on  the  hanging  plate  is  greater 
than  the  pressure  in  the  holder.  The 
man-lid  may  then  be  removed.  FIG.  310.— THE  LIVESEY  MAN-LID. 


GASHOLDER  TANKS 

Gasholder  tanks  as  now  erected  may  primarily  be  classified  under  three  head- 
ings :— 

(a)  Buried  tanks,  the  top  of  which  is  approximately  level  with  the  prevailing 
ground  line. 

(6)  Tanks  entirely  aboveground,  in  which  the  top  of  the  concrete  foundation 
is  on  a  level  with  the  ground  line. 

(c)  Semi-buried  tanks  which  are  constructed  partly  below  ground  and  which 
are  "  banked  up  "  level  with  their  upper  edge  with  the  material  taken  from  the 
excavation. 

There  is,  in  addition,  a  fourth,  but  uncommon,  type,  in  which  the  floor  of  the 
tank  is  constructed  upon  piers  or  arches  above  ground  level,  the  space  below  being 
employed  as  a  storehouse  or  for  some  similar  purpose.  With  one  or  two  possible 
exceptions,  it  may  be  stated  that  types  (a)  and  (c)  are  almost  solely  constructed  from 
brick,  concrete  or  reinforced  concrete,  while  steel,  reinforced  concrete,  or  cast  iron 
are  employed  in  all  tanks  aboveground.  From  the  point  of  view  of  modern  practice, 
•cast  iron  may  be  dismissed  from  consideration  forthwith.  It  was  employed  largely 
some  three  or  four  decades  ago  at  a  time  when  rolled  steel  plates  were  extremely 
costly  and  could  not  be  obtained  of  sufficient  thickness  for  large  tanks.  The  number 
of  brick  tanks  which  are  to  be  found  to-day,  particularly  in  connexion  with  the  older 
gasholders,  is  chiefly  the  outcome  of  the  fact  that  in  years  past  it  was  not  deemed 
advisable  to  construct  cast-iron  tanks  above  a  certain  capacity  ;  and,  as  the  cost  of 
.steel  was  still  prohibitive,  the  only  alternative  was  that  of  excavating  a  hole  and 
lining  it  with  a  shell  capable  of  retaining  water  and  of  sufficient  stability  to  withstand 
the  forces  acting  against  it. 


454 


MODERN   GASWORKS   PRACTICE 


BRICKWORK  AND  CONCRETE  TANKS 

Tanks  composed  of  brickwork  are,  in  general,  of  two  descriptions : — 
(a)  Puddled  tanks. 
(6)  Rendered  tanks. 

The  main  difference  between  the  two  types  is  in  the  means  introduced  for 
ensuring  that  the  tank  shall  be  water-tight.  Brickwork,  per  se,  is  not  impervious  to 
water,  hence  recourse  must  be  had  to  some  means  of  making  it  so.  Water-tightness 
is  ensured  either  by  jacketing  the  tank  on  its  exterior  surface  with  a  layer  of  puddled 
clay  (hence  the  expression  "  puddled  tank  "),  or  by  coating  the  interior  of  the  tank 


..       -.>,,      .-.    m—»-    it 

FIG.  311. — PART  SECTION  OF  MASONRY  TANK  SHOWING  "  DUMPLING." 

with  a  thin  rendering  (about  £  inch  to  1  inch  thick)  of  neat  cement  or  rich  mortar, 
in  which  case  it  will  be  a  "  rendered  tank."  A  half  section  of  a  typical  puddled 
tank,  showing  how  the  work  of  excavation  is  lessened  by  leaving  a  "  dumpling,"  is 
shown  in  Fig.  311.  In  constructing  a  tank  of  this  description,  it  is  usual  to  build 
up  the  brickwork  in  short  lifts  and  then  to  fill  in  with  puddle  between  the  wall  and 
the  ground.  The  puddle  may  consist  of  pure  clay,  but  some  engineers  at  one 
time  preferred  to  introduce  a  small  proportion  of  sand  or  mould  in  order  to  prevent 
cracking  when  the  material  dries  off.  As  each  layer  of  puddle  is  filled  in  it  must  be 
well  moistened  and  thoroughly  "  punned."  It  will  be  noticed  from  the  accom- 
panying figure  that  the  puddle  is  spread  entirely  over  the  "  dumpling." 

An  elementary  consideration  of  the  static  pressure  of  water  is  sufficient  to  show 
that  the  bursting  pressure  at  any  section  due  to  the  contained  water  varies  in  direct 
ratio  to  the  depth  of  the  section  below  the  surface.  Thus  for  determining  the 
pressure  due  to  water  at  any  point  the  following  simple  formula  may  be  used  :— 

P  =wd 

where  P  =  pressure  in  Ibs.  per  square  foot 
ID  =  weight  of  a  cubic  foot  of  water 
d  =  depth  below  surface  in  feet. 


THE   STORAGE   OF   GAS  455 

In  a  circular  tank  the  radial  thrust  will,  therefore,  gradually  increase  from  the 
surface  of  the  water  to  the  bottom  of  the  tank ;  in  other  words,  the  magnitude  of  the 
pressure  is  shown  by  the  line  AB  (Fig.  312)  and  the  thickness  of  the  tank  wall  may 
theoretically  be  graduated  in  accordance  with  this  line.  Theoretically,  no  thickness 
at  all  is  required  at  the  surface  of  the  water,  but  for  reasons  too  obvious  to  need 
explanation  such  a  condition  is  impossible  in  practice. 

From  a  consideration  of  the  simple  formula  previously  given,  it  might  be  presumed 
that  the  calculation  of  the  stresses  in  a  masonry  tank,  and  hence  its  design,  would 
be  a  comparatively  easy  operation.  Such,  however,  is  by  no  means  the  case,  for 
many  factors  of  an  uncertain  nature  »(such  as  the  cohesive  resistance  of  the  brick- 
work) are  introduced^  with  the  result  that  a  purely  theoretical  method  of  design  is 
extremely  difficult  of  application.  There  is  no  doubt  that  in  the  design  of  a  masonry 
tank  some  sound  theoretical  treatment  would  prove  of  immense  value,  but  at  present 
there  is  no  such  treatment  at  our  disposal,  with  the  result  that  practical  experience 
and  the  lesson  of  precedents  chiefly  influence  the  designer.  Herein  lies  one  of  the 
paramount  advantages  of  the  steel  tank,  our  knowledge  of  which  permits  of  a  reason- 
ably accurate  computation  of  the  stresses  to  which  it  will  be  subjected.  Occasionally 
one  may  come  across  the  most  elaborate  calculations  for  arriving  at  the  factor 
of  safety  obtaining  in  a  masonry  tank  worked  out  to  two  decimal  places.  The 
inconsistency  of  such  procedure  should  be  self-evident  when  it  is  remembered  that 
the  theories  so  far  laid  down  for  the  treatment  of  these  tanks  are  merely  the  result 
of  surmise,  and  are  built  up  from  a  series  of  pure  structural  considerations,  which 
probably  have  no  relation  to  actual  conditions. 

Some  forty  years  ago  a  series  of  formulae  were  deduced  wherewith  it  was 
proposed  to  calculate  the  stability  of  masonry  tanks.  These  formulae  are  still 
in  use  at  the  present  day,  and  may  be  found  quoted  in  modern  text  books.  A 
cursory  examination  of  the  formulae,  however,  would  appear  to  show  that  they 
contain  such  elementary  errors  as  that  of  assuming  the  horizontal  pressure  of 
earth  constant  for  all  depths  and  independent  of  the  distance  below  the  surface. 
Any  one  acquainted  with  the  theories  of  Rankine  and  others  will  perceive  the  absurdity 
of  such  an  assumption.  It  must  be  realized  that  the  brick  tank  of  a  gasholder  is 
not  subjected  to  a  simple  bending  moment  as  in  the  case  of  an  ordinary  retaining 
wall,  but  stresses  are  set  up  on  the  lines  of  those  occurring  in  the  plates  of  a  cylindrical 
boiler,  and  instead  of  the  wall  tending  to  tilt  over  from  the  base  the  whole  undergoes, 
in  almost  all  cases,  slight  circumferential  stretching,  whilst  there  is  also  a  strain  in 
the  vertical  direction.  As  in  the  case  of  the  steel  tank,  which  receives  support  from 
the  bottom  curb  and  floor  space,  so  is  the  brick  wall  restrained  to  a  certain  extent 
by  its  adhesion  to  the  foundations. 

H.  W.  Alrich,  in  a  communication  to  the  American  Gas  Institute,  has  shown 
that  the  restraint  exercised  by  the  foundation  will  reach,  approximately,  a  distance 
up  from  the  bottom  of  the  tank  equal  to  I-  to  J  of  the  total  depth  of  the  tank.  Accord- 
ingly, if  in  the  diagram  (Fig.  312)  the  dotted  line  represents  the  tank  as  constructed, 
the  position  and  shape  it  will  take  up  when  filled  with  water  will  be  of  the  nature  of 
that  shown  by  the  full  line.  As  before  explained,  the  theoretical  thickness  at  the 


456 


MODERN   GASWORKS   PRACTICE 


Restraint 
due  to  excess 
thickness 


top  is  nil,  but  the  thickness  allowed  in  practice  is  such  as  to  prevent  a  certain  amount 
of  stretching  in  the  upper  portion ;  thus  there  is  in  reality  a  restraining  influence  at 
both  top  and  bottom. 

The  author  has  made  a  particular  study  of  the  various  mathematical  treatments 
which  have  been  suggested  for  the  computation  of  the  stresses  induced  in  masonry 
tanks,  but  finds  that  on  examination  they  are  more  likely  to  be  misleading  rather 
than  of  any  service  in  design.  It  is  believed  that  hitherto  the  vertical  strain  in  the 
tank,  an  extremely  important  factor  in  the  evolution  of  a  theoretical  treatment,  has 
never  been  considered,  and  there  is  no  doubt  that  the  difficulty  of  ascertaining  this 
with  accuracy  is  not  encouraging. 

The  nature  of  the  assistance  of  the  earth  backing  has  givgn  rise  to  a  good  deal 
of  controversy,  some  authorities  believing  it  to  be  active,  and  some  passive.  There 
can  be  little  doubt,  however,  that  once  the  tank  has  been  put  under  stress  the  ring 

tension  and  circumferential  stretching  induced  are 
followed  by  a  passive  resistance  in  the  earth.  The 
earth,  moreover,  is  a  somewhat  uncertain  quantity. 
To  emphasize  this  it  is  only  necessary  to  refer  to  the1 
well  known  work  of  Sir  Benjamin  Baker.  In  the 
course  of  his  examination  of  dams  and  river  walls, 
Baker  found  that  in  some  cases  it  was  possible  to 
thrust  down  an  iron  bar  some  considerable  distance 
between  the  earth  and  the  brickwork,  showing  that- 
the  latter  was  receiving  practically  no  assistance 
from  the  earth  backing.  Such  conditions  might 
well  be  found  in  the  case  of  semi-buried  tanks  hav- 
ing the  earth  mounded  up  against  the  upper  portion. 
In  such  instances  there  maybe  some  tendency  for  the 
earth  to  slide  backwards  and  so  relieve  the  pressure 
against  the  wall. 

An  old-fashioned  rule,  due  to  Wyatt,  for  the 
proportion  of  brick  tanks,  is  as  follows : — 
Thickness  of  concrete  walls  =  y1^  the  depth  of  tank 

„  piers  =    1     „       „       „       „ 

Width         „  piers  =    J     ,,       „       ,,       „ 

This  refers  to  tanks  up  to  150  feet  diameter  and  36  feet  deep. 

For  very  large  holders,  a  brick  or  concrete  tank  is  most  suitable,  so  long  as  a 
firm  foundation,  free  from  water,  can  be  obtained.  Concrete  tanks,  with  cement 
and  ballast  at  reasonable  prices,  are  cheaper  than  the  brick  variety,  and  they  are 
in  almost  all  cases  rendered  on  the  'interior.  The  brick  tank  possesses  advantages 
over  the  concrete  tank  in  that  less  skill  is  required  in  its  construction,  there  is  less 
initial  stress  due  to  shrinkage,  and  less  liability  towards  cracking  caused  by  any 
variation  in  the  temperature  of  the  water.  The  method  of  connecting  up  inlet  and 
outlet  pipe  to  a  gasholder  with  masonry  tank  and  the  construction  of  the  "  dry 
well"  is  shown  in  Fig.  311. 


Restraint  due 


Fia.  312. — SHOWING   EFFECT  OF 

WATER  PRESSURE  ON  MASONRY 

TANK. 


THE   STORAGE   OF   GAS  457 

STEEL  TANKS 

It  may  be  laid  down  as  a  general  rule  that  unless  a  gasholder  is  upwards  of  two 
million  cubic  feet  capacity  a  steel  tank  is  undoubtedly  the  most  economical.  In 
modern  practice  the  steel  tank  finds  considerable  favour  in  all  cases  except  where 
the  holder  is  of  considerable  size,  although  steel  was  employed  for  the  New  York 
holder  tank,  which  has  a  diameter  of  250  feet  and  a  depth  of  46  feet.  The  capacity 
of  this  holder  is  ten  million  cubic  feet. 

Steel  tanks  may  be  said  to  possess  the  following  advantages  : — 

(a)  They  are  usually  less  expensive  than  masonry  tanks. 

(b)  A  foundation  which  might  be  classed  as  unsuitable  for  a  sunk  tank  may  be 
sufficiently  stable  for  a  steel  tank. 

(c)  Quickness  and  ease  of  construction. 

(d)  Owing  to  the  ease  of  determining  the  working  stresses  with  reasonable 
accuracy  there  is  no  difficulty  in  designing  the  tank  with  a  known  factor  of  safety. 

(e)  Steel  is  reliable  under  stress.     The  properties  of  brickwork  and  concrete  in 
this  direction  are  uncertain. 

(/)  The  tank  can  be  readily  tested  and  made  water-tight,  for  the  whole  is  acces- 
sible for  inspection.  As  regards  the  floor  plating,  it  is  usual  to  put  the  sections 
together  on  bearers  which  raise  it  a  short  distance  above  the  foundation.  When 
the  floor,  bottom  curb  and  bottom  row  are  riveted  up,  the  tank  is  filled  with  water 
to  a  depth  of  about  one  foot.  Any  joint  "  weeps  "  are  then  attended  to  and  the 
whole  is  afterwards  let  down  on  to  its  foundation. 

(g)  Masonry  tanks  must  be  allowed  to  stand  for  some  time  after  completion 
before  they  are  filled  with  water.  The  steel  tank  may  be  filled  immediately  it  is 
finished. 

(h)  With  the  steel  tank  there  is  no  initial  stressing  caused  by  shrinkage  or  change 
of  temperature. 

(i)  The  failure  of  a  steel  tank  is  extremely  rare. 

On  the  other  hand,  the  advocates  of  the  masonry  tank  point  out  that : — 

(a)  The  life  of  a  steel  tank  is  short  in  comparison  with  that  of  the  masonry 
tank. 

(b)  The  exterior  of  a  steel  tank  is  affected  by  corrosion,  thus  fairly  frequent 
painting  is  essential.     This  periodical  expense  is  not  incurred  with  the  buried  tank. 
(It  should  be  noted,  in  this  connection,  that  the  inside  surface  of  the  plates,  being 
always  under  water,  is  not  affected  by  corrosion,  except  to  a  certain  extent  at  and 
above  the  surface  of  the  water.) 

(c)  The  crown-rest  framing  for  the  holder  bell  will  be  more  costly,  owing  to  the 
impracticability  of  employing  a  dumpling. 

(d)  The  guide  standards  of  the  holder  will  be  longer. 

THE  DESIGN  OF  TANKS 

When  the  erection  of  a  gasholder  is  contemplated,  trial  holes  must  be  bored 
down  on  the  site  in  order  to  determine  the  suitability  of  the  ground  for  foundations. 
A  good  foundation  is  absolutely  essential,  not  only  to  provide  for  the  satisfactory 


458 


MODERN   GASWORKS   PRACTICE 


working  of  the  holder,  but  to  ensure  economy  in  construction.  Where  brick  tanks 
have  been  already  built,  care  should  be  taken  that  the  ground  in  their  vicinity  is  not 
violently  disturbed.  Instances  can  be  pointed  to  where  such  tanks  have  been  cracked 
by  the  driving  of  piles  near  by.  Good  ballast  may  occasionally  be  obtained  from 
the  subsoil,  and  in  this  case  it  may  prove  more  economical  to  provide  a  concrete 
tank,  even  though  the  holder  be  comparatively  small. 

As  regards  the  foundations  for  steel  tanks,  the  circular  slab  is  usually  levelled 
off  flush  all  over,  but  some  designers  prefer  that  the  concrete  should  slope  up  to  a- 
height  at  the  centre  of  4  or  5  inches  above  the  level  at  the  periphery.  It  is  said 
that  in  this  manner,  if  there  is  any  sinking  of  the  ground  underneath,  the  bottom 
will  assume  a  level  bedding.  It  would  seem,  however,  that  if  any  rise  is  to  be  given 
this  should  be  allowed  at  the  periphery  (where  the  whole  of  the  weight  of  side  sheets 
and  standards  is  concentrated)  rather  than  at  the  centre.  As  in  the  case  of  the 
masonry  tank,  the  gas  inlet  and  outlet  pipes  are  led  up  through  the  floor  of  the  steel, 
tank,  but  they  should  be  constructed  from  wrought  iron  and  with  the  open  ends 
bell-mouthed.  The  floor  plates  themselves  are  comparatively  thin  and  should  be 
rectangular,  except  for  those  in  the  outer  row,  which  are  made  to  the  circular  shape 
of  the  tank  and  are  usually  slightly  thicker.  Outside  floor  plates  are  usually  -fa 
inch  to  -|  inch,  with  the  curb  row  \  inch  thick. 


FIG.  313. — BOTTOM  CURBS  FOE  TANKS. 


The  bottom  row  of  the  side  sheeting  is  composed  of  the  heaviest  plates  in  the 
structure,  the  thickness  of  the  plate  depending  upon  the  depth  of  the  tank,  but  in 
exceptional  cases  being  as  much  as  2J  inches.  These  plates  are  connected  to  the 
tank  floor  by  means  of  a  bottom  curb  which  usually  consists  of  a  single  angle  placed 
internally  or  externally,  or  of  a  double  angle,  as  shown  in  Fig.  313.  By  far  the  most 
common  practice,  however,  is  to  provide  the  internal  angle  alone.  In  the  treatment 
of  gasholder  tanks  it  is  generally  assumed  that  a  certain  amount  of  restraint  is- 
exercised  by  the  bottom  curb  and  floor  plates  in  preventing  the  circumferential 
stretching  of  the  bottom  row  when  the  tank  is  under  load.  This,  no  doubt,  is  the 
case,  but  a  series  of  experiments  carried  out  with  scale  models  at  one  of  the  London 
colleges  has  shown  that  the  magnitude  of  this  restraint  is  actually  very  small. 

In  designing  tanks  for  gasholders  it  is  usual  to  calculate  the  required  thickness 
of  the  side  plate  by  considering  the  head  of  water  as  equal  to  the  depth  above  the 
centre  of  gravity  of  the  plate,  and  not  the  depth  to  the  base  of  the  plate.  The 
author  is  of  the  opinion  that  such  a  practice  is  inadvisable  and  that  the  depth  to 


THE   STORAGE   OF   GAS 


459 


the  base  of  each  row  should  be  taken  when  the  stability  of  that  row  is  being 
calculated. 

When  arriving  at  the  thickness  of  the  bottom  row  of  side  plates,  some  allow- 
ance is  often  made  by  designers  for  the  restraint  due  to  the  floor  plating.  The  most 
ready  means  of  doing  this  is  to  make  a  deduction  from  the  total  depth  of  the  tank. 
This  deduction  usually  amounts  to  about  3  per  cent  of  the  depth.  It  should  be 
borne  in  mind,  however,  that  owing  to  the  restraining  influence  of  the  bottom  curb, 
however  slight  this  may  be,  the  bottom  row  plates  will  be  prevented  to  a  certain 
extent  from  joining  in  the  expansion  of  the  remainder  of  the  ring.  Accordingly, 
bending  stresses  will  be  set  up  in  the  lowest  ring  plates,  for  which  due  allowance 
should  be  made. 

So  far  as  the  author  is  aware  the  largest  steel  tank  erected  is  that  at  the  Kings- 


Extended  Plate 


FIG.  314. — TOP  CURB  FOR  STEEL  TANK  (SPIRAL  HOLDER). 

bridge  works  of  the  New  York  Consolidated  Gas  Company.  The  holder  has  a 
capacity  of  10  million  cubic  feet, whilst  the  diameter  of  the  tank  is  251  feet  3  inches, 
with  a  depth  of  46  feet  4  inches.  The  tank  shell  is  composed  of  nine  rows  of  plates, 
the  lowest  row  of  which  is  2^  inches  thick,  the  plates  being  4  feet  in  height.  The 
topmost  ring  consists  of  \  inch  plates,  6  feet  in  height.  All  the  vertical  seams — and 
here  it  should  be  pointed  out  that  in  the  riveting  of  tanks  it  is  the  vertical  seams 
which  require  particular  forethought,  the  horizontal  joints  give  little  trouble — are 
double  butt-joints  designed  so  that  a  portion  of  the  rivets  are  acting  in  single  shear 
and  some  in  double  shear,  and  so  arranged  that  the  efficiency  of  the  joint  is  93  per 
cent.  All  the  horizontal  seams  are  lap  joints  single-riveted  with  rivets  varying  ir> 


460  MODERN   GASWORKS   PRACTICE 

size  from  If  inch  at  the  base  to  1  inch  for  the  top  row.  Both  plates  and  butt- straps 
are  bevelled-edged,  this  or  ordinary  planing  being  commonly  carried  out  to  facilitate 
caulking.  The  tank  bottom  is  formed  of  -|  inch  plates,  20  feet  long,  and  7  feet  6  inches 
wide,  connected  together  by  |  inch  rivets.  The  curb  row  of  plates  is  f  inch  thick. 
The  bottom  curb  consists  of  an  external  angle,  8  inches  by  8  inches  by  1^  inch  thick, 
put  together  in  twenty-six  sections  joined  by  angle  connexion  plates.  The  upper 
curb  of  the  tank  consists  of  a  horizontal  plate  \  inch  thick  attached  to  the  tank 
shell  by  a  5  inch  by  5  inch  by  \  inch  angle,  and  is  stiffened  round  its  outer  edge  by  a 
12  inch  channel. 

A  point  of  importance  in  the  design  of  holders  with  steel  tanks  is  that  of  ensuring 
that  the  tank  structure  shall  itself  be  as  independent  as  possible  of  the  stresses  set 
up  in  the  guide  framing.  Any  such  stresses  should  be  carried  down,  not  to  the  top 
curb  of  the  tank,  but  to  the  foundation.  This  precept  is  often  overlooked,  with  the 
result  that  the  tank  plates  are  subjected  to  stresses  for  which  they  were  not  designed. 
A  frequent  error  in  design  is  that  of  carrying  the  diagonal  cross-bracing  of  the  panel 
down  to  the  top  curb  of  the  tank,  thus  leaving  the  tank-panels  unbraced.  As  regards 
the  guiding  of  the  bell  in  the  tank  it  is  customary  to  provide  intermediate  rails 
between  those  fixed  at  the  main  upright  stanchions.  The  construction  of  the  top 
curb  for  a  steel  tank  to  take  a  spirally  guided  bell  is  shown  in  Fig.  314. 

THICKNESS  or  SIDE  PLATES 

The  necessary  thickness  for  side  plates  is  readily  calculated  by  considering  the 
pressure  on  the  ring  at  a  certain  depth  due  to  the  head  of  water,  and  by  treating 
the  tank  as  an  ordinary  thin  cylinder  subjected  to  internal  pressure. 

The  following  is  the  formula  employed,  which  may  easily  be  deduced  from  first 
principles  : — 

P  X  D  =  2/te 

P.D 

or  £= 

2fe 

Where  P  =  pressure  due  to  water  in  Ibs.  per  square  inch. 
D  =  diameter  of  tank  in  inches. 

/  =  allowable  working  stress  (usually  5£  tons  per  square  inch). 
t  =  thickness  of  plate  in  inches. 

e  =  the  efficiency  of  the  vertical  riveted  joints.  Up  to  90  per  cent,  for 
large  holders.     For  small  holders  it  ranges  from  75  to  85  per  cent. 
The  pressure  P  is  found  as  before  explained,  namely, — 

P  =  wd  Ibs.  per  square  foot,  where 
<w=  weight  of  a  cubic  foot  of  water  =  62  "4  Ibs. 
d  =  depth  below  surface  of  the  bottom  of  the  plate. 

Thus,  to  calculate  the  required  thickness  of  the  bottom  row  for  a  tank  30  feet 
deep  and  150  feet  diameter  we  haye — 

P=  wd=  624  X  30—  1872  Ibs.  per  square  foot  =  13  Ibs.  per  square  inch. 

13  X  (150  X  12)       100       .  A_  .     , 

then  t  =  — — ;  v  —  =  1-05  inches 

2  X  5£X  2240        90 


THE   STORAGE   OF   GAS 


461 


3"  Lap  ' 


Planrd  Top  and 
Bottom  (inly 


D 


V*> 

I T 


•®- 

~-&i~® 


VIM 

*•£$& 

r^y^J^kooiv 


W-'W 


j^LJU 

>  <&I%-@! 


Second  Row  Plate, 
(say)  I"  Thick 


Bottom.  Plate, 
Planed  all  Round. 
>say)l"  Thick 


•Outside  Cover  Plate  |" 


-Inside  Cover  Plate  |" 

.  Outside  Cover. 
Planed  all  Round 
and  Caulked. 


As  regards  the  calculation  of  the  efficiency  of  riveted  joints  this  is  a  simple 
procedure,  which  may  be  found  described  in  full  in  many  books  on  structural  design. 
The  rivets  should  be  checked  for  their  stability  in  the  way  of  resisting  shearing  and 
bearing  stresses,  whilst  the  plate  at  the  joints  must  be  sufficiently  strong  to  preclude 
tearing,  shearing  or  bursting  through  the  edge.  The  efficiency  of  the  joint 

_  Least  strength  of  joint 
Strength  of  solid  plate 

It   has    been  SECTION 

shown  by  experi- 
ment that  in  many 
instances  the  ulti- 
mate resistance  of 
tank  plates  is  less 
than  the  stress  that 
would  be  necessary 
to  overcome  the 
friction  at  the 
joints,  and  that  the 
friction  is  so  great 
that  within  the 
limits  of  working 
stress  there  is 
neither  shear  in 
the  rivet  nor  bear- 
ing stress  against 
the  shank.  Such  a 
condition  applies, 
of  course,  to  those 
cases  where  the 
rivet  exactly  fits 
the  hole,  and  the 
work  and  design  is 
of  a  first  class 
character.  An 
example  of  a  typi- 
cal vertical  seam  butt-joint  is  shown  in  Fig.  315. 

TANKS  WITH  BULGING  SIDES 

One  of  the  chief  objections  to  the  steel  tank,  when  its  depth  becomes  appreciable, 
is  the  necessity  for  providing  plates  of  abnormal  thickness,  which  are  often  difficult 
to  obtain-  and  cumbersome  to  handle.  For  this  reason  it  has  been  suggested  that 
the  tank  should  be  designed  in  such  a  manner  as  to  permit  of  the  side  plates  being 
of  uniform  thickness  throughout,  whilst  the  very  thick  plates  common  to  the  cylin- 
drical tank  could  be  dispensed  with.  The  principle  involved  is  that  of  curving  or 


-®- 


Bottom  Curb 
6  *  6 '  x  1"  Angle. 


Jt 


^  Planed  and  Caulked 
ELEVATION 
FIG.  315. — VERTICAL  SEAM  BUTT  JOINT  FOR  STEEL  TANK. 


462 


MODERN   GASWORKS   PRACTICE 


FIG.  316. — BONNET'S  TANK 
WITH  BULGING  SIDES. 


FIG.  317. 


bulging  the  sides  of  the  tank  in  such  a  manner  that 
the  horizontal  stresses  due  to  the  head* of  water  are 
transmitted  to  the  top  curb  (which  must,  accordingly, 
be  of  stout  construction)  and  to  the  tank  floor.  A 
tank  of  this  description,  designed  on  Bonnet's  system, 
is  seen  in  Fig.  316.  It  will  be  noticed  that  vertical 
posts  are  placed  at  intervals  round  the  tank  ring.  The 
static  pressure  of  the  water  is  then  transformed  into 

(a)  A   horizontal   pull    at    the    base,  this  being 
balanced  by  the  tension  in  the  floor  plates  (see  Fig. 
317). 

(b)  A    pull    at    the 
upper  surface  of  the  tank 
acting    at    a  tangent  to 
the  curve  at  that  point. 
This  tangential  pull  will 
be  distributed  as  a  ver- 
tical downward  thrust  in 
the  columns,  and  by  a 
horizontal  outward  radial 
thrust  in  the  top  ring  curb. 

The  principle  of  the  method  is  undoubtedly  interesting,  but  it  has  made  little 
headway  in  practice.  The  most  interesting  example  of  a  tank  constructed  on  these 

lines  is  that  at  Simmering,  in  connexion  with 
a  holder  having  a  capacity  of  nearly  5|  million 
cubic  feet. 

F.  S.  Cripps  has  designed  a  tank  for  attain- 
ing the  same  object  in  which  the  sheets,  in- 
stead of  being  bulged,  are  fluted.  The  sides 
are  split  up  into  a  series  of  circular  arcs  of 
much  smaller  radius  than  that  of  the  tank, 
with  vertical  posts  at  the  intersections,  the 
whole  being  united  by  a  ring  girder  at  the  top. 
As  pointed  out  by  Cripps,  however,  the  greatest 
objection  to  this  type  of  construction  is  the 
enormous  stress  on  the  top  girder  (see  Fig.  318.) 
FIG.  318. — CKIPPS'  FLUTED  TANK. 

REINFORCED  CONCRETE  TANKS 

Reinforced  concrete  as  a  material  of  construction  for  gasholder  tanks  has  not 
made  any  great  headway.  The  inherent  principle  of  reinforced  structures  is  that 
whilst  the  compressive  stresses  may  be  apportioned  to  the  concrete  the  tensional 
forces  must  be  provided  for  by  the  insertion  of  steel.  In  the  gasholder  tank  the 
stresses  are  almost  wholly  tensional,  with  the  result  that  the  amount  of  steel  required 
for  reinforcement  is  no  less  than  that  required  for  the  construction  of  a  complete 


THE   STORAGE   OF   GAS  463 

steel  tank.  This  statement  must  be  qualified  by  the  fact  that  the  efficiency  of  the 
riveted  joint  must  be  taken  into  account,  but  in  large  steel  tanks  the  heavier  plates 
n:ay  have  a  joint  efficiency  of  90  per  cent.  It  is  agreed  that  even  though  this  be 
the  case  the  steel  work  is  merely  inserted  in  place  in  the  concrete  and,  consequently, 
there  is  no  riveting  to  be  done.  It  is  clear,  however,  that  the  cost  of  the  concrete 
itself  would  be  greater  than  the  expense  incurred  for  riveting. 

When  under  construction  there  is  considerable  difficulty  in  getting  the  rein- 
forcing bars  into  position,  also  in  ensuring  that  the  concrete  forms  a  homogeneous 
mass  round  bars  which  must  of  necessity  be  closely  pitched.  The  factor  of  safety 
must  depend  largely  on  these  two  conditions,  for  if  the  tank  is  carelessly  constructed 
the  tensional  stresses  will  be  falling  upon  the  concrete  instead  of  on  the  steelwork. 
The  result  is  that  cracks  and  leaks  make  their  appearance.  One  of  the  great 
drawbacks  to  this  type  of  tank  is  the  time  taken  in  construction,  this  being — from 
the  time  of  commencement  until  the  tank  is  ready  for  service— -nearly  twice  that 
required  with  a  similar  tank  made  from  steel.  Probably  the  largest  reinforced  tank 
in  existence  is  that  erected  at  New  York.  This  tank  is  300  feet  in  diameter  and 
48  feet  3  inches  deep. 

It  should  be  mentioned  that  reinforced  concrete  tanks  develop  minute  hair 
cracks  when  the  stress  in  the  tensile  members  becomes  excessive,  in  fact  when  the 
stress  in  the  steel  reaches  6,000  Ibs.  per  square  inch.  The  New  York  City  Board,  as 
a  result  of  investigations  with  reinforced  concrete  cylinders,  have  limited  the  unit 
stress  in  the  reinforcement  of  water- retaining  structures  to  8,000  Ibs.  per  square  inch. 

THE   COST  OF  GASHOLDERS 

A  large  holder  is  much  cheaper  per  unit  of  volume  than  is  one  of  smaller  dimen- 
sions. So  far  as  the  actual  weight  of  metal  is  concerned  the  holder  of  light  construc- 
tion is  not  necessarily  the  cheapest,  for  there  will  in  all  probability  be  additional 
labour  expenditure  which  will  more  than  absorb  any  saving  in  material.  Increasing 
the  number  of  lifts,  moreover,  actually  renders  the  holder  bell  more  costly  ;  but,  in 
this  case,  there  would  be  a  reduced  expenditure  on  tank  and  guide-framing,  so  that 
a  three-lift  holder  will  usually  be  cheaper  than  a  two-lift  holder  of  equal  capacity. 
For  very  small  holders  a  single  lift  is,  as  a  general  rule,  the  cheapest  form  of 
construction. 

Per  ton  of  metal  the  average  cost  of  a  gasholder  varies  between  £19  and  £22  in 
normal  times,  this  figure  including  the  whole  structure  and  steel  tank.  As  regards 
the  individual  items,  much,  of  course,  depends  on  size  and  design,  but  the  total 
outlay  will  be  accounted  for  somewhat  as  follows  : — 

Bell,  complete     .         .         .         .         .         .         .         .     35  to  45  per  cent,  of  total 

Guide  framing    .         .         .         .         .         .         .  18  to  23        ,,  „ 

Tank  (steel)         . 35  to  45 

Some  interesting  examples  of  the  cost  of  existing  holders  are  given  here  ;  but 
it  must  be  remembered  that  as  these  holders  were  erected  at  a  time  when 
materials  and  labour  were  less  expensive,  the  costs  cannot  be  taken  as  indicative 


464 


MODERN   GASWORKS   PRACTICE 


Holder 

and  tank 

(Thousands). 


Cost  in  £. 


Tanks. 

Holder  Capacity, 
in  Thousands. 


of  present-day  figure*  : — 


1  500  

—  18000  
14000  

800  

12000  
1  1  000  
10000  
9  000  

7  000  

6.000  

6  000  

'4000  
3.000  

2.000.  

1.000  

East  Greenwich  . 
Manchester    . 
Berlin 
Vienna 


Approximate       Cost  per  1,000 
capacity,      cubic  feet  contents. 

12  million  cubic  feet  £550 

10£     „         „         „  £500 

8      „        „        „  £13    9    0 

8£    „  £7  13    0 


Single  lift  gasholders,  with  guide-framing, 
of  small  dimensions  (say  up  to  50,000  cubic 
feet  capacity)  cost  from  £25  to  £28  per  1,000 
cubic  feet,  but  if  of  the  spiral  type  the  cost 
would  be  about  25  per  cent.  less. 

Two-lift  holders  of  about  a  quarter  of  a 
million  cubic  feet  capacity  range  from  £16  to 
£20  ;  or  if  spirally  guided  about  £10  per  1,000 
cubic  feet.  Holders  of  the  most  usual  size  as 
found  in  provincial  works,  those  of  2  to  3  million 
capacity,  cost  from  £9  to  £12  per  1,000  cubic 
feet. 

The  cost  of  the  tanks  varies  in  accord- 
ance with  their  size  and  design,  and  with  the 
prevailing  costs  of  steel,  brick  and  cement. 

The  following  are  typical  instances  : — 


FIG.  319. 


For  2  million  cubic  feet  holder — 

Cost  per  1,000  cubic  feet  holder 
capacity 

Cost  per  cubic  foot  tank  capacity "     . 
For  1  million  cubic  feet  holder — 

Cost  per  1,000  cubic  feet 

Do.  for  £  million  cubic  feet  holder     . 
Average  cost  of  tank  for  1  million  cubic 
feet  holder 

Per  1,000  cubic  feet  capacity. 


Per  cubic  foot  tank  capacity 


Brick  and  Puddle.    Concrete  Rendered. 


£5  10s.  to  £7 
4d.  to  6d. 


£6  5s. 


£5  to  £6  5s. 
4-2rf.  to  5-3d. 


£5  15s. 


5-1d. 


Steel. 


£4  to  £4  5s.1 


£4  10s.1 
£5  5s.1 


£4  10s.  +  17s.  6rf. 

foundations  = 

£5  7s.  6rf. 


1  Add  foundations  17s.  6d.  to  35s.  in  each  case. 


The  diagram  (Fig.   319)  shows  the  relation  between  the  cost  of  gasholders 
and  their  capacity,  also  the  cost  of  steel  tanks. 


THE    STORAGE   OF   GAS  465 

THE   PRESSURE   THROWN  BY  A   GASHOLDER 

The  pressure  thrown  by  a  gasholder  is  dependent  upon  the  weight  of  the  floating 
portion  and  its  diameter.  Thus,  if  the  total  weight  of  the  bell,  including  the  weight 
of  the  water  in  the  lutes,  is  W  tons  and  the  diameter  of  the  holder  is  D  feet  the 
pressure  may  be  calculated  as  follows : — 

549  W 
Maximum  pressure  in  inches  of  water  =  -— — 

A  single  lift  holder  usually  throws  from  3  to  4  inches  of  water  pressure,  while 
in  the  case  of  a  telescopic  holder  the  top  lift  will  throw  about  the  same  amount,  with 
each  succeeding  lift  throwing  about  2  inches.  When  dealing  with  multiple  lift 
holders  a  figure  comparing  very  closely  with  the  actual  pressure  thrown  in  practice 
may  be  obtained  by  considering  the  total  weight  and  the  mean  diameter  of  the 
holder,  although  this  is  not  strictly  accurate.  Theoretically,  the  weight  of  the  bell, 
when  the  holder  is  fully  inflated,  acts  on  the  greatest  area,  i.e.  the  area  obtained  by 
considering  the  diameter  of  the  lowest  lift.  In  practice,  the  pressure  thrown  by 
the  inner  lift  alone  is  the  chief  consideration. 

THE   CONTAMINATION   OF   GAS   IN   HOLDERS 

It  occasionally  happens  that  coal  gas,  although  found  to  be  perfectly  clean  at 
the  outlet  of  the  purifiers,  shows  decided  traces  of  sulphuretted  hydrogen  at  the 
holder  outlet.  Fortunately,  such  an  occurrence  is  comparatively  rare  in  this  country, 
but  one  London  company  experienced  considerable  annoyance  in  this  respect  some 
few  years  ago.  The  pollution  of  gas  in  this  way  is  the  result  of  the  spontaneous 
production  of  sulphuretted  hydrogen  in  the  gasholders,  or,  less  commonly,  in  station 
meters.  Although  no  positive  reason  can  be  ascribed  for  the  formation  of  the 
impurity,  it  seems  extremely  probable  that  it  may  be  due  to  the  presence  of  certain 
micro-organisms,  or  to  an  electrolytic  action  set  up  by  the  iron  plates.  It  is,  of 
course,  a  recognized  fact  that  certain  bacilli  characteristic  of  ordinary  water  possess 
the  property  of  decomposing  definite  salts  (such  as  calcium  sulphate,  present  in  the 
water),  with  the  evolution  of  sulphuretted  hydrogen.  A  series  of  experiments  con- 
ducted on  water  taken  from  a  gasholder  tank  seemed  to  corroborate  the  organic 
theory,  the  bacteria  deriving  their  necessary  food  supply  from  dead  iron  organisms. 
In  the  case  of  the  London  company,  complete  immunity  from  the  trouble  was  obtained 
after  the  bacilli  had  been  destroyed  by  means  of  a  germicide,  such  as  sulphate  of 
copper.  The  French  investigator,  M.  Guillet,  has  concluded  that  contamination  is 
also  caused  by  exposure  of  the  gas  to  a  clean  iron  surface  resulting  from  the  detach- 
ment of  rust.  He  has  shown  that  in  the  presence  of  the  bare  metal  the  carbon 
di  sulphide  in  the  gas  reacts  with  carbon  dioxide  and  water,  with  the  liberation  of 
sulphuretted  hydrogen.  The  remedy,  suggested  in  this  case,  however,  is  somewhat 
inconvenient,  as  the  holder  must  temporarily  be  put  out  of  action.  It  entails  the 
soldering  of  zinc  sheets  to  the  iron  plates  at  definite  places,  when  galvanic  action 
checks  the  formation  of  the  sulphuretted  hydrogen. 


H  H 


CHAPTER    XVIII 
WATER  GAS 

MANUFACTURE,     ENRICHMENT,    AND    USE 

IN  the  year  1793  Lavoisier  discovered  that  when  steam  is  passed  over  incandescent 
carbon,  the  carbon  is  oxidized  and  carbon  monoxide  and  hydrogen  are  produced. 
The  modern  water-gas  plant  is  wholly  dependent  upon  this  principle. 

Water  gas  must  be  looked  upon  as  essentially  an  auxiliary  to  coal  gas,  and 
in  this  capacity  it  has  been  adopted  by  a  large  number  of  gas  undertakings  as  a 
means  of  providing  for  increase  of  business  and  occasional  sudden  demands.  Water 
gas,  manufactured  on  the  Lowe  principle,  was  introduced  into  this  country  in  1890, 
although  prior  to  this  it  was  experimented  with  for  some  fifty  years  without  any  very 
favourable  or  convincing  results.  Water  gas  was,  at  the  outset,  adopted  on  account 
of  its  comparative  cheapness  as  an  enriching  medium  as  compared  with  the  methods 
then  in  vogue.  Its  introduction  naturally  met  with  a  good  deal  of  opposition  from 
the  conservative  gas  engineer,  but  its  utility  gradually  became  self-evident,  insomuch 
that  it  is  now  present  in  most  town  gas  to  an  extent  of  from  15  to  30  per  cent, 
by  volume.  At  the  present  time  carburetted  water  gas  is  looked  upon  rather  as 
a  useful  auxiliary  for  dealing  with  the  "  peak  "  load ;  for  enrichment  has  largely 
lost  its  significance  in  present-day  practice.  The  rise  in  price  of  the  enriching 
oil  is  largely  due  to  the  extended  uses  to  which  residue  petroleums  are  now  put, 
and  to  the  comparatively  high  freightage  rates  prevailing.  Instead  of  costing 
about  2d.  per  gallon,  as  in  1910,  the  price  of  the  oil  has  in  the  last  year  or  so 
risen  to  as  much  as  5d.,  or  even  I0d.,  per  gallon.  For  this  reason  the  proportion  of 
water  gas  intermixed  with  coal  gas  has  in  many  cases  undergone  considerable 
reduction  ;  in  fact,  some  works  did  at  one  time  cease  to  make  it  altogether. 
The  annual  output  of  water  gas  in  the  whole  world,  nevertheless,  amounts  to 
about  150,OCO  million  cubic  feet. 

The  benefits  derived  from  the  use  of  water  gas  as  an  auxiliary  to  coal  gas  may 
be  summarized  as  follows  : — 

1 .  Low  capital  outlay  per  unit  of  capacity.     Including  relief  holder  the  outlay 
on  a  carburetted  water-gas  plant  of  large  capacity  would  amount  to  about  one-third 
that  entailed  by 'a  coal-gas  plant  of  similar  capacity. 

2.  The  ground  space  occupied  by  the  plant  is  considerably  smaller  than  the  area 
covered  by  equivalent  coal-gas  plant.     The  ratio  of  the  areas  required  may,  in 
fact,  be  so  great  as  9  to  1. 

4«6 


WATER   GAS  467 

As  regards  ground  area  required,  Shelton  gives  the  following  figures  : — 

CAPACITY  or  PLANT.  GROUND  AREA  REQUIRED. 

100,000  cubic  feet  per  diem  .          .          .4  square  feet  per  1,000  cubic  feet. 
200,000          „                „  3-5 

400,000          „  „  2-75 

600,000          „  „  ...     2  to  2-5    „ 

7  to  10  million  „  ...     1-25  to  1-5,, 

These  figures  include  scrubbers  and  condensers,  but  not  boiler  house,  engine 
room,  or  relief  holder. 

3.  Sudden  demands,  such  as  those  due  to  fog  and  other  unforeseen  contingencies, 
may  be  easily  and  quickly  coped  with.     A  water-gas  plant  may  be  picked  up  from 
cold  in  rather  more  than  three  hours.     Retort  benches  require  three  days  to  bring 
them  up  to  working  heats. 

4.  The  expense  of  retort  benches  constantly  under  slow  firing  is  obviated. 

5.  The  quality  of  the  gas  made  is  easily  regulated  to  the  requirements  of  the 
moment. 

6.  The  proportion  of  water  gas  intermixed  with  the  coal  gas  may  be  varied  in 
accordance  with  the  demand  for  coke.     Thus,  a  water-gas  plant  possesses  a  con- 
trolling influence  over  the  coke  market,  and  large  stocks  of  this  by-product  may 
to  some  extent  be  avoided. 

7.  The  fact  that -a  considerable  proportion  of  the  gas  may  be  manufactured  from 
coke  in  lieu  of  coal  places  the  works  in  a  position  of  rather  greater  independence 
so  far  as  coal  supplies  are  concerned. 

8.  In  these  days  of  labour  upheavals  the  small  amount  of  manual  work  required 
with  a  water-gas  plant  is  a  prominent  consideration.     The  item  of  wear  and  tear, 
both  in  the   direction  of  labour  'and   materials,   is  low  in  comparison  with  the 
ordinary  machine-charged  horizontal  retorts. 

9.  The  sulphur  impurities  in  the  gas  are  low  in  comparison  with  the  same 
impurities  in  crude  coal  gas.     As  regards  sulphuretted  hydrogen,  crude  coal  gas 
contains  on  an  average  500  to  800  grains  per  100  cubic  feet,  and  crude  water  gas 
120  grains.     Of  carbon  disulphide  and  other  sulphur  compounds  coal  gas  contains 
from  35  to  50  grains,  and  carburetted  water  gas  10  to  15  grains  per  100  cubic  feet. 

10.  In  many  instances  carburetted  water  gas  has  proved  itself  effective  in 
diminishing  trouble  from  naphthalene  deposits.     It  is  said  that  the  carburetted 
gas  acts  as  a  solvent  vehicle  for  naphthalene  and,  accordingly,  prevents  its  precipi- 
tation from  the  coal  gas.     Much,  however,  would  appear  to  depend  upon  the  tem- 
perature at  which  the  carburettor  and  superheater  are  operated,  for  if  the  light  oil 
vapours  are  submitted  to  too  great  a  temperature,  over-cracking  will  occur  and  the 
virtue  of  the  gas  as  a  naphthalene  sedative  is  likely  to  be  lost.     Again,  of  course, 
much  will  depend  upon  the  proportion  in  which  the  carburetted  gas  is  present.     At 
any  rate,  water  gas  as  a  naphthalene  eradicator  must  not  by  any  means  be  looked 
upon  as  infallible. 

As  regards  the  inherent  disadvantages  of  water  gas  it  is  not  possible  to  compile 
a  very  formidable  list ;    but,  first,   mention   must  be  made  of  the  very  high  per- 


468  MODERN   GASWORKS   PRACTICE 

centage  of  noxious  gas,  carbon  monoxide,  which  it  contains,  the  proportion  amount- 
ing to  three  or  four  times  as  much  as  that  to  be  found  in  coal  gas.  The  objection  is,  no 
doubt,  one  which  is  largely  discounted  in  the  present  day,  for  the  many  years'  experi- 
ence of  water  gas  shows  no  tendency  towards  any  increase  in  the  number  of  deaths 
from  asphyxiation.  A  further  disadvantage  lies  in  the  fact  that,  at  the  time  of 
writing,  the  expense  of  manufacture  of  carburetted  gas  is  greater  than  that  of  coal 
gas  owing  to  the  very  considerable  increase  in  the  cost  of  oil. 

The  smooth  operation  of  a  water-gas  plant  may  be  quickly  upset  by  the  intro- 
duction of  an  inferior  coke,  and  its  somewhat  sensitive  nature  in  this  respect  is  liable 
to  give  trouble  in  those  works  where  a  high-class  coal,  with  a  low  ash-content,  is 
not  always  procurable.  In  some  works  it  is  customary  to  set  aside  the  coke  from 
the  higher  quality  coals  for  the  exclusive  use  of  the  water-gas  plant.  It  is  frequently 
urged  as  a  merit  of  carburetted  water  gas  that  its  permanence  is  a  great  recommenda- 
tion in  preventing  any  deterioration  of  or  deposition  from  the  district  gas  as  it  passes 
through  the  street  mains.  On  the  other  hand,  the  author's  experience  goes  to  show 
that  any  slight  imperfection  in  the  fixing  chambers,  or  any  insufficiency  of  condensa- 
tion, may  be  followed  by  a  very  appreciable  drop  in  illuminating  power  during  the 
passage  of  the  gas  through  the  district  mains.  Deterioration  of  the  kind  may,  how- 
ever, be  guarded  against  by  operating  both  carburettor  and  superheater  at  their 
correct  temperatures,  and  by  attending  to  the  periodical  cleaning  and  re-chequering 
of  these  vessels.  The  condensers,  too,  must  operate  on  efficient  lines,  so  that  the 
temperature  of  the  gas  is  reduced  as  near  as  possible  to  that  of  the  atmosphere  before 
entering  the  oxide  purifiers. 

S.  Carter  has  pointed  out  that  7C°  Fahr.  may  be  looked  upon  as  a  critical 
temperature  in  the  process,  and  that  with  gas  leaving  the  purifiers  at  this  temperature 
oil  will  be  precipitated  in  the  holders. 


THEORY  OF  MANUFACTURE 

The  generation  of  water  gas  depends  upon  the  action  of  steam  upon  red-hot 
carbon,  the  latter  being  present  in  the  form  of  coke  (containing  about  80  per  cent, 
of  carbon).  As  is  well  known,  water,  or  steam,  cannot  be  decomposed  by  the  action 
of  heat  alone  ;  but  if  subjected  to  heat  in  the  presence  of  a  reducing  agent  the  oxygen 
will  combine  with  this  agent,  with  the  evolution  of  hydrogen  in  the  free  state. 
Heated  carbon  possesses  a  greater  affinity  for  oxygen  than  does  the  hydrogen  with 
which  the  oxygen  is  combined  in  the  form  of  steam.  Hence  the  sequence  of  reactions 
which  result.  The  oxygen  of  the  steam  combines  in  the  first  place  with  the  carbon 
to  form  carbon  dioxide,  and  some  carbon  monoxide.  Thus,  in  the  lower  portions 
of  the  fuel  bed  we  have  the  following  reactions  : — 
(a)  C  +  2H20  =  C02+  2H2. 
(6)  C+H20  :=  CO+H2. 

According  to  the  generally  accepted  theory  the  carbon  dioxide  is  subsequently 
"  reduced,"  by  combination  with  another  carbon  atom,  during  its  travel  through 
the  remainder  of  the  fuel  bed  : — 

(c)  C02-f  C  = 


WATER   GAS  469 

The  reduction  of  carbon  dioxide  to  carbon  monoxide  in  this  manner  is,  how- 
ever, never  quite  complete,  with  the  result  that  from  3  to  4  per  cent,  of  the  former 
gas  is  found  in  the  finished  product.  The  quantity  of  carbon  monoxide  formed  by- 
direct  reaction  at  the  base  of  the  fuel  bed  will  largely  depend  upon  the  temperature 
prevailing  in  that  portion. 

A  study  of  the  thermal  nature  of  these  reactions  is  important,  for  in  this  way 
the  principle  of  the  operation  of  modern  apparatus  may  be  best  explained.  The 
reaction  (a)  for  the  production  of  C02  absorbs  heat,  as  also  does  (6)  which 
accounts  for  the  direct  formation  of  CO.  By  far  the  greatest  proportion  of  heat  is, 
however,  absorbed  by  the  so-called  reducing  action  (c).  The  first  reaction  (a)  will  not 
occur  at  temperatures  less  than  about  1,100°  Fahr.,  whilst  slightly  higher 
temperatures  still  are  required  for  reactions  (&)  and  (c).  It  may  be  seen,  then, 
that,  in  order  that  the  required  reactions  shall  take  place,  the  fuel  bed  must,  in  the 
first  instance,  be  raised  to  a  definite  temperature  ;  and,  in  order  that  the  reactions 
may  continue,  the  temperature  must  be  maintained  above  a  certain  minimum  in  the 
face  of-  a  series  of  endothermic  changes.  Means  wherewith  the  temperature  is 
maintained  by  intermittent  operation  is  now  almost  universally  adopted — the 
gasmaking  period,  having  a  duration  of  a  few  minutes,  being  followed  by  a  spell 
of  heat  recuperation,  technically  known  as  the  "  blow."  At  the  completion  of  the 
gasmaking  "  run,"  the  steam  is  shut  off  from  the  fuel  bed,  and  a  blast  of  air  takes 
its  place.  The  oxygen  of  the  air,  combining  with  the  hot  carbon,  is  then  directly 
converted  into  C02 : — 

(d)  Blow  reaction  : — 

C  -f  02=  C02. 

As  is  well  known,  this  reaction  is  exothermic  in  nature,  the  approximate  quan- 
tity of  heat  evolved  amounting  to  13,500  B.Th.U.  per  Ib.  of  coke  consumed.  By 
the  continuance  of  the  "  blow  "  for  a  definite  period,  usually  rather'  more  than 
half  that  of  the  gasmaking  "  run,"  the  temperature  of  the  bed  and  of  the  surround- 
ing brickwork  is  restored.  The  part  played  by  the  substantial  firebrick  lining  must 
not  be  overlooked.  These  walls,  once  they  are  heated  through,  form  a  reserve  of 
heat  which  is  available  to  be  drawn  upon  during  the  gasmaking  period. 

WATER-GAS  SYSTEMS 

The  systems  which  have  been  introduced  for  the  purpose  of  manufacturing 
water  gas  may  be  classified  under  the  following  three  headings : — 

(1)  The  Continuous  System. 

(2)  The  Intermittent  System. 

(3)  The  Neat-Oxygen  Method. 

Of  these,  the  intermittent  method  is  the  only  one  to  which  serious  considera- 
tion is  given  to-day.  The  continuous  system,  in  which  it  was  sought  to  replace 
the  lost  heat  by  independent  external  firing,  received  much  attention  in  the  early 
days  of  water  gas  ;  and  was  in  one  respect  to  be  commended,  in  that  it  endeavoured 
to  provide  for  the  uninterrupted  manufacture  of  the  gas  and  obviated  the  periods 


470  MODERN   GASWORKS   PRACTICE 

of  blowing.  Practical  difficulties,  heat  losses  by  radiation,  and  general  inefficiency, 
however,  soon  sounded  its  knell,  with  the  result  that  there  are  no  examples  of  the 
method  now  extant.  The  intermittent  process,  with  "  run  "  and  "  blow  "  suc- 
ceeding each  other  at  regular  intervals,  has  shown  itself,  by  the  test  of  time,  to  be 
the  only  practicable  method. 

A  scientific  and  by  no  means  impracticable  system  is  that  embodying  the  use 
of  neat  oxygen.  The  process  operates  on  continuous  lines  and  results  in  a  gas  prac- 
tically free  from  nitrogen,  but  containing  from  65  to  70  per  cent,  of  carbon  monoxide. 
Steam  is  admitted  to  the  base  of  th«  generator  in  the  ordinary  manner  ;  and,  along 
with  it,  is  passed  a  stream  of  pure  oxygen.  In  this  way,  whilst  steam  is  combining 
with  a  portion  of  the  carbon  to  form  water  gas,  the  heat  lost  by  the  endothermic 
nature  of  the  reactions  is  replaced  by  the  exothermic  combination  of  the  oxygen 
with  part  of  the  carbon.  If  steam  and  oxygen  are  regulated  in  accordance  with 
theoretical  requirements  the  process  will  proceed  with  little  trouble.  The  chief 
drawback,  which  has  as  yet  prevented  the  system  from  making  any  great  headway, 
is  the  impossibility  of  obtaining  oxygen  at  a  price  which  would  permit  the  gas  to 
compare  in  cost  with  that  produced  by  the  more  general  methods. 

Some  mention  should  be  made  here  of  the  distinction  between  carburetted  water 
gas  and  oil  gas,  the  latter  misnomer  being  still  in  somewhat  common  use  for  the 
former  product.  Oil  gas,  in  the  .true  sense  of  the  name,  is  the  gaseous  mixture  of 
hydrocarbon  vapours  resulting  from  the  direct  conversion  of  oil  into  gas,  in  an  iron 
retort,  such  as  takes  place  in  the  Peebles  and  Pintsch  processes.  In  this  way 
a  gas  having  an  illuminating  power  of  from  60  to  70  candles  is  obtained.  An  im- 
portant feature  of  such  processes  is  the  further  washing  of  the  gas  in  oil,  whereby 
any  vapours  not  rendered  permanently  gaseous  are  removed.  This  oil  is  returned 
to  the  retort  again  and  again,  the  residue  remaining  behind  as  a  coke.  In  this 
country  the  process  has  chiefly  been  applied  in  connexion  with  the  well-known 
Scottish  shale  oils,  about  100  cubic  feet  of  gas  being  obtained  from  one  gallon  of  the 
oil.  In  countries  where  a  mineral  oil  is  only  obtained  with  some  difficulty  the  gas 
has  been  produced  from  animal  dr  vegetable  varieties. 

TYPES  OF  WATER-GAS  PLANT 

The  plants  now  in  use  for  the  purpose  of  generating  water  gas  are  many  and 
varied.  In  general,  however,  the  apparatus  may  be  classified  under  two  distinct 
headings,  namely  : — 

(a)  Plants  employing  an  enriching  agent,  i.e.  carburetting  plants. 

(6)  Plants  in  which  no  enrichment  of  the  gas  takes  place,  i.e.  "blue"  gas 
plants. 

It  must  be  understood,  however,  that  with  the  carburetting  plant  "  blue  "  . 
gas  may,  if  so  desired,  be  readily  produced,  and  in  the  same  way  many  of  the  recog- 
nized "  blue  "  plants  are  now  fitted  with  a  small  carburettor,  which  enables  them 
to  yield  enriched  gas.  In  addition  to  the  above  apparatus,  mention  must  be 
made  of  the  more  modern  and,  as  yet,  little  known  plant  known  as  the  "  Methane- 
Hydrogen  "  system,  and  such  plants  as  that  of  Strache,  which  entail  the  complete 


fc 

a 


471 


472 


MODERN   GASWORKS   PRACTICE 


gasification  of  coal.  These  are  discussed  later.  Of  the  carburetting  plants,  that 
originally  introduced  in  the  United  States  by  Lowe,  and  improved  by  Humphreys 
and  Glasgow,  has  undoubtedly  gained  the  greatest  popularity. 

The  apparatus  (Fig.  320)  consists  of  a  generator,  carburettor,  superheater, 
oil-heater,  washer  or  seal,  and  condenser.  The  generator,  carburettor,  and  super- 
heater are  cylindrical  in  shape  ;  the  shells  are  formed  of  f-inch  steel  plates,  and  are 


FIG.  321. — A  SMALL  HUMPHREYS  AND  GLASGOW  INSTALLATION. 

lined  with  special  firebricks.  In  order  to  reduce  to  a  minimum  the  heat  lost  by 
radiation,  an  annular  space,  about  two  inches  wide,  is  left  between  the  shell  and  the 
firebrick  lining,  and  this  is  tightly  packed  with  slag  wool.  The  generator  is  charged 
through  a  circular  door  in  the  top ;  cast-iron  doors  being  provided  at  the  base  for 
the  removal  of  the  clinker.  A  two-way  pipe,  the  function  of  which  will  be  explained 
later,  connects  the  generator  and  carburettor.  Fitted  to  the  top  of  the  carburettor 


WATER   GAS 


473 


is  a  centrifugal  oil  spray.  A  steam  pump,  connected  with  the  storage  tank, 
delivers  oil  to  the  distributor  at  a  pressure  of  about  60  Ib.  per  square  inch,  the  oil 
having  been  previously  passed  through  the  heater  and  considerably  raised  in  tem- 
perature. Both  the  carburettor  and  superheater  are  filled  with  firebricks  laid 
chequer-wise,  the  disposition  of  the  bricks  affording  extensive  heating  surface  for 
the  permanent  gasification  of  the  oil.  A  stack  valve  is  placed  at  the  top  of  the 


FIG.  322. — OPERATING  FLOOR  OF  HUMPHREYS  AND  GLASGOW  PLANT,  SHOWING  INTERLOCKING  VALVE- 
GEAR,  GAUGES,  ETC. 

superheater,  and  through  this  the  final  products  are  expelled  during  the  "  blow  "  ; 
during  the  "  run  "  this  valve  is  closed,  and  the  carburetted  gas  makes  its  way 
through  the  remainder  of  the  apparatus.  As  will  be  seen  from  the  figure,  the  oil 
heater  is  placed  in  the  outlet  pipe  from  the  superheater  and  meets  the  full  volume 
of  the  hot  gas.  With  the  exception  of  clinkering,  the  plant,  in  all  but  the  smaller 
installations,  is  entirely  manipulated  from  an  elevated  floor,  flush  with  the  top  of 
the  generator,  and  all  valves,  levers  and  gauges  are  collected  at  this  level.  Any 


474 


MODERN   GASWORKS   PRACTICE 


risk  of  the  operator  moving  the  wrong  levers  is  obviated  by  the  insertion  of  a  special 
interlocking  valve-gear. 

A  special  feature  of  the  apparatus  is  the  reversal  of  the  "  run  "  in  the 
generator,  so  that  steam  may  be  admitted  either  below  the  coke-bed  or  above  it  ; 
it  is  to  enable  this  to  be  done  that  the  two-way  pipe,  previously  referred  to,  is 
employed. 


FIG.  323. — AN  INSTALLATION  OF  TWO  HUMPHREYS  AND  GLASGOW  PLANTS,  SHOWING  DOWN-PIPES  FROM 

SUPERHEATERS,  AND  WASHERS. 

Experience  shows  that  if  steam  is  continually  admitted  to  the  base  of  the 
generator,  in  time  the  lower  portion  of  the  fuel  bed,  which  has  continually  to  perform 
the  heaviest  duty  of  decomposition,  becomes  cool  and  inactive,  the  steam  con- 
densing instead  of  being  converted  into  gas.  The  succeeding  "  blow,"  therefore, 
instead  of  rekindling  the  fire,  chills  down  the  lower  layers  of  coke  still  more.  To 
rectify  this,  after  every  few  runs  the  steam  is  admitted  above  the  fuel  and  makes 
its  way  downwards  and  thence  to  the  carburettor  as  usual.  The  reversal  of  flow  is 


WATER   GAS 


475 


completely  effected  in  one  movement,  the  valves  being  controlled  by  interlocking 
gear  which  renders  confusion  or  mistake  impossible.  The  function  of  the  washer, 
which  corresponds  to  the  hydraulic  main  of  the  coal-gas  plant,  is  to  provide  a  safety 
seal  which  precludes  the  gas  from  being  pushed  back  into  the  superheater  (by  the 
pressure  thrown  by  the  relief  holder)  during  the  periods  of  the  "  blow."  The 
washers  are  well  illustrated  in  Fig.  323.  The  purpose  of  the  scrubber  and  the  con- 
densers is  to  remove  the  vesicles  of  tar  and  oily  matter  which  remain  suspended 
in  the  gas,  and  to  cool  the  gas  down  to  a  normal  temperature  prior  to  condensation. 
The  Humphreys  and  Glasgow  plants  are  made  in  sizes  ranging  from  100,000 
cubic  ft.  to  3  million  cubic  ft.  per  twenty-four  hours.  One  of  the  most  interesting 
installations  is  that  at  the  Beckton  gasworks.  In  this  case  the  plant,  consisting  of 


FIG.  324. — BECKTON  PLANT,  SHOWING  LEVERS  FOR  HYDRAULIC  OPERATION. 

five  sets,  has  a  maximum  capacity  of  18  million  cubic  feet  per  diem,  and  the  whole 
of  the  operation  is  performed  by  means  of  hydraulic  power,  which  controls  all  valves, 
at  a  pressure  of  500  Ib.  per  square  inch.  The  gasmaker  attached  to  each  unit  has 
merely  to  stand  at  his  station,  and  by  the  turn  of  a  lever  can  change  from  cycle  to 
cycle.  The  working  floor  of  the  Beckton  plant  is  seen  in  Fig.  324. 

SINGLE  SUPERHEATER  PLANTS 

A  good  deal  of  attention  has,  been  given  to  the  single  superheater  type  of  plant, 
some  examples  of  which  now  exist  in  this  country.     In  such  plants  the  carburettors, 
and  superheater  are  merged  into  a  single  vessel  of  rather  larger  capacity  than  the 
superheater  of  the  more  common  plant.    There  is  some  conflict  of  opinion  as  to  which 


476 


MODERN   GASWORKS   PRACTICE 


c_J 


BLAST  PIPCINLET 


SECTION  ONC  D 
FIG.  325. — SINGLE  SUPERHEATER  PLANT,  MERRIFIELD-WESTCOTT-PEARSON  TYPE. 

method  is  to  be  preferred  from  the  point  of  view  of  getting  the  utmost  efficiency 
from  the  oil,  but  the  single  superheater  plant  is  certainly  less  costly  in  the  first  place. 


WATER   GAS 


477 


FIG.  326. — THE  MERRIFIELD-WESTCOTT-PEARSON  PLANT,  SHOWING  SINGLE  SUPEKHEATEB. 

In  this  type  of  plant,  it  has  been  said  that  by  introducing  the  oil  at  an  intermediate 
point  in  the  superheater  the  more  volatile  constituents  separate  out  immediately, 
ascend,  and  make  their  escape  before  undergoing  decomposition.  Meanwhile, 
the  heavier  constituents  of  the  oil  fall  to  the  base  of  the  vessel  and  are  then  swept 


478 


MODERN   GASWORKS   PRACTICE 


forward  again  by  the  current  of  water  gas  entering  from  the  generator,  traversing 
the  entire  height  of  the  chamber. 

The  most,  important  plant  operating  on  this  principle  in  this  country  is  that 
known  as  the  Merrifield-Westcott-Pearson.  As  before  explained,  it  differs  from 
the  double  superheater  plant  in  that  the  carburettor  and  superheater  consist  of  one 
vessel,  and  the  oil  is  injected  at  three  distinct  points  round  the  periphery  of  the  vessel 
instead  of  from  one  spray  at  the  top.  The  oil,  moreover,  is  sprayed  in  a  direction 
contrary  to  that  of  the  gas,  whereas  in  the  Humphreys  plant  it  travels  with  the  gas. 
An  additional  feature  is  that  the  hot  gas  passes  through  the  condenser  before  being 
scrubbed,  while  in  the  original  installations  the  main  valves  were  cooled  by  a  system 

of  water  circulation.  The  advo- 
cates of  the  double  superheater 
system  point  out  that  the  primary 
consideration  affecting  the  econo- 
mical gasification  of  oil  is  that  the 
oil  shall  be  exposed,  at  a  high  rate 
of  travel,  to  a  prc-per  fixing  sur- 
face at  a  moderate  and  carefully 
adjusted  temperature.  Accord- 
ingly, this  surface  must  consist  of 
length  in  the  direction  in  which  the 
gas  travels,  rather  than  of  cross- 
section  ;  for  the  vapours  must 
never  approach  a  condition  of  rest 
in  contact  with  the  hot  surface  in 
the  fixing  chambers.  For  this 
reason,  the  oil  should  be  intro- 
duced with,  and  not  against  the 
current  of  gas. 


REGENERATOR 


GENERATOR 


GENERATOR 


FIG.  327.— THE  "  K.  &  A."  BLUE  GAS  PLANT. 


"  BLUE  "  WATER-GAS  PLANTS 

Of  the  "  blue "  water-gas 
plants,  the  Kramers  and  Aarts 
apparatus,  and  also  the  Dell- 
wik  plant,  have  been  extensively 

adopted  on  the  Continent,  and  both  plants   have    made   some   headway   in   this 
country. 

The  former  plant — known  as  the  "  K.  &  A." — is  unique  in  that  the  generator 
is  composed  of  two  vessels,  and,  while  during  the  "  run  "  these  are  used  in  series, 
during  the  "  blow  "  they  are  worked  in  parallel.  It  is  found  that  this  device  permits 
the  period  of  blowing  to  be  about  one-quarter  of  that  required  in  the  plants  previ- 
ously described,  and  therefore  the  time  of  gasmaking  is  correspondingly  increased. 
A  section  of  the  apparatus  is  depicted  in  Fig.  327,  and  by  referring  to  this  the  system 
of  working  can  be  readily  followed.  It  will  be  noticed  that  between  the  two  gener- 


WATER   GAS 


479 


FIG.  328.—"  K.  &  A."  PLANT,  LATER  FORM. 


ators,  a  third  vessel,  known  as  a  regenerator,  is  interposed.     During  the  "  blow," 
this  is  heated  up  by  the  hot  gases   from  the  fires.     During  the    "  run,"    steam 


480 


MODERN   GASWORKS   PRACTICE 


is  introduced  to  one  of  the  generators  and  is  converted  into  carbon  dioxide  and 
monoxide ;  it  then  traverses  the  regenerator,  where  the  surplus  steam  is  split  up 
and  the  gas  super-heated  ;  finally  it  makes  its  way  through  the  second  generator,  in 
which  the  carbon  dioxide  is  reduced  to  carbon  monoxide.  For  the  next  run  the 
direction  of  the  steam  is  reversed,  that  is,  the  final  generator  now  becomes  the 
first. 

This  system  combines  a  shallow  fuel  bed  for  the  blast,  together  with  a  deep  fire 
and  long  contact  with  the  incandescent  coke  during  the  "  run."     The  fact  that  while 


REGENERATOR 


GENERATOR 


GENERATOR 


FIG.  328A.— SECTIONAL  PLAN  ON  FIG.  328. 


during  the  "  blow  "  a  shallow  bed  of  fuel  is  required  and  during  the  "  run  "  a  deep 
fire  is  desirable  has  proved  a  difficulty  to  many  designers  of  water-gas  plant,  but 
the  introduction  of  the  split  generator  has  effectively  overcome  this. 

It  is  interesting  to  note  that  in  the  large  hydraulically  controlled  installation 
at  the  Beckton  works  the  units  are  fitted  with  generators  on  the  "  twin  "  principle, 
and  that  by  the  movement  of  a  lever  the  generators  may  be  set  during  the  "  run  " 
for  operating  either  in  series  or  in  parallel.  In  this  case  the  generators  are  no 
more  shallow  than  is  the  ordinary  single  generator,  and  the  chief  advantage  lies  in 


WATER   GAS 


481 


the  fact  that  when  they  are  operated  in  parallel  during  the  "run "the  capacity  of 
the  plant  is  increased  by  some  25  to  30  per  cent.  On  the  other  hand,  when  the 
demand  for  gas  may  be  less  they  can  be  steamed  in  series,  when  a  rather  better 
quality  gas  containing  a  smaller  percentage  of  C02  will  be  obtained. 

The  Dellwik 
blue-gas  plant 
(Fig.  329),  while 
yielding  a  gas 
very  similar  to  f~^_  imm\/im, 
that  produced  in 
the  "K.  &  A." 
apparatus, 
materially  differs 
from  it  in  con- 
struction. In  this 
case  there  is  a 
single  generator 
preceded  by  a 
s  u  p  erheater 
through  which  the 
steam  passes  be- 
fore entering  the 
generator.  It  will 
be  noticed  that 
the  door  at  the 
top  of  the  genera- 
tor performs  the 

double  duty  of  a  stack  valve  and  charging  door  for  replenishing  the  coke.  The 
gas  passes  direct  from  the  generator  to  the  superheater,  and  thence  through  a  coke 
scrubber.  As  in  the  other  plants,  an  interlocking  valve-gear  precludes  the  possibility 
of  any  danger  which  might  arise  from  carelessness  on  the  part  of  the  operator. 

In  this  process  the  air  supply  from  the  blower  is  most  carefully  regulated,  and 
the  level  of  the  fuel  bed  should  be  kept  constant. 


—.^ 


Scrubber       Superheater  ^  Generator 

FIG.  329. — DELLWIK  "  BLUE  "  GAS  PLANT. 


PRODUCTS  OF  THE  "  BLOW  " 

In  the  Dellwik  plant  an  endeavour  is  made  to  so  regulate  the  air-blast  and  fuel 
bed  that  the  products  of  the  "  blow  "  consist  almost  solely  of  C02  and  nitrogen. 
When  air  is  admitted  to  the  base  of  a  deep  fuel  bed,  C02  is  formed  in  large  proportion 
in  the  first  place,  but  on  travelling  through  the  remainder  of  the  fuel,  it  is  partially 
reduced  to  carbon  monoxide,  so  that  a  semi-producer-gas  results.  The  percentage 
of  CO  present  in  the  products  varies  inversely  with  the  speed  of  the  blast,  and  directly 
with  the  depth  and  temperature  of  the  fuel  bed.  At  first  sight  the  presence  of  CO' 
might  appear  to  be  a  distinct  disadvantage,  for  it  is  produced  by  allowing  an  endo- 

1 1 


482  MODERN   GASWORKS   PRACTICE 

thermic  reaction  to  take  place  during  the  period  when  maximum  heat  expulsion 
is  desirable.  Moreover,  by  burning  carbon  to  C02  about  three  times  as  much  heat 
is  evolved  as  when  it  is  burnt  to  CO  only.  It  has  to  be  borne  in  mind,  however,  that 
in  the  majority  of  plants  the  case  of  succeeding  apparatus  comes  in  for  consideration. 
For  instance,  in  the  Lowe  plant  the  generator  is  followed  by  two  vessels  which  them- 
selves must  be  raised  to  a  high  temperature  ;  whilst  in  the  "  K.  &  A."  plant  there 
is  the  regenerator  to  be  heated  up.  Thus,  the  producer  gas  issuing  from  the  generator 
(or  generators,  in  the  case  of  the  twin  plants)  is  burnt,  by  admitting  a  small  quan- 
tity of  secondary  air  from  the  blast  main,  in  the  succeeding  vessels,  maintaining 
these  at  the  desired  temperature.  The  average  composition  of  the  "  blow  "  gases 
issuing  from  the  generator  when  the  fuel  bed  of  the  latter  is  moderately  deep  is 
as  follows  : — 

Carbon  monoxide     .      .   .         .         .       '  .          .          .17  per  cent,  by  volume. 

Carbon  dioxide         ......'         .          .          .10         ,,  ,, 

Nitrogen          .         .  .         .         .         .         .     73        ,,  „ 

Traces  of  hydrogen  and  methane  may  also  be  found. 

Working  with  a  fuel  bed  of  6  feet  6  inches  in  the  Lowe  type  plant,  the  author 
finds  the  following  result : — 

"BLOW"    GASES 

CO2.  CO. 

End  of  1st  minute     .      .   .          .         .          .     18-6  per  cent.  2-9  per  cent. 

2nd       „         .      '."•.,.       .         .          .     14-6       „  9-4 

'.       „        3rd  .         .         .         .          .     12-0        „  16-4 

4th  .         .--  ...        •'.:-    7-6       „  19-8 

From  this  it  will  be  seen  that  the  quality  of  the  producer  gas  is  gradually  under- 
going improvement  as  the  blow  proceeds  and  the  fire  becomes  hotter. 

The  main  overhead  blast  pipe,  with  connexions  leading  to  the  carburettor  and 
superheater,  is  seen  in  Fig.  321. 

As  regards  apparatus  for  providing  the  blast,  this  in  the  early  days  of  water  gas 
invariably  consisted  of  an  open  fan  driven  by  a  high-speed  reciprocating  steam 
engine.  The  speed  of  the  fan  is  usually  in  the  neighbourhood  of  2,000  revolutions 
per  minute.  For  modern  work  the  reciprocating  engine  has  been  almost  entirely 
superseded  by  the  steam  turbine  ;  or,  in  isolated  cases,  by  electric  motors.  The 
de  Laval  steam  turbine  coupled  to  a  Sturtevant  fan  (Fig.  330)  is  the  most  common 
form  in  use.  In  this  case  the  speed  of  the  turbine  is  geared  down  in  a  ratio  of  10 
to  1  so  as  to  give  the  requisite  speed  at  the  blower.  Another  form  of  blower  wrhich 
is  coming  into  favour  is  that  designed  on  the  Rateau  principle,  which  appears  to 
provide  somewhat  greater  efficiency  in  the  direction  of  blast.  As  regards  the  electric 
drive,  this  has  proved  quite  suitable,  but  it  cannot  be  said  that  it  affords  the  same 
elasticity  as  is  obtained  with  the  steam  motor.  The  question  of  providing  a  "  posi- 
tive "  blast  is  one  which  has  engaged  the  designers  of  water-gas  plant.  The  ordinary 
open  fan,  such  as  the  Sturtevant  type,  is  not  a  pressure-raising  device,  and  merely 
propels  a  current  of  air  through  spaces  which  may  be  open  to  it.  Accordingly,  if 


WATER   GAS 


483 


the  main  outlet  pipe  is  suddenly  closed  the  pressure  will  rise  from  1  inch  to  2  inches 
only.  "  Positive  "  blowers,  on  the  other  hand,  are  pressure- raising  devices  enclosed 
by  a  casing.  Thus,  if  the  main  outlet  was  closed  the  pressure  in  the  casing  and 
pipe  would  go  on  building  up  until  something  gave  way,  or  the  engine  was  pulled 
up.  The  most  notable  example  of  these  blowers  is  the  Roots  type.  Dellwik  plants 
Invariably  employ  a  positive  blast,  and  in  this  way  it  is  said  that  rekindling  can  be 
done  more  rapidly,  and,  therefore,  the  duration  of  the  "  blow  "  may  be  curtailed. 
When  such  a  blower  is  used,  however,  it  is  essential  to  fit  a  safety-valve  on  the 
main  blast  pipe. 

Explosions  in  the  blast  main,  occasionally  resulting  in  the  wrecking  of  the  fan, 
.are  by  no  means  an  unknown  occurrence.     They  are  essentially  the  outcome  of  a  badly 


FIG.  330. — TURBO-DRIVEN  WATKR-GAS  FAN. 

fitting  hot-gas  valve,  i.e.  the  valve  between  blast  main  and  generator,  which  may 
permit  a  small  portion  of  water  gas  to  get  by  during  the  down  runs.  This  gas, 
meeting  with  the  air  in  the  blast  main,  forms  an  explosive  mixture,  which  may  be 
ignited  by  a  spark  from  the  fan.  A  safety  appliance,  designed  to  minimize  the 
damage  caused  by  such  a  contingency,  is  shown  in  Figs.  331  and  332.  It  consists 
of  a  cast-iron  flap  swinging  in  a  special  box  which  is  attached  to  the  outlet  of  the 
fan.  During  the  time  when  the  blower  is  at  work  the  flap  remains  in  the  position 
shown.  Should  any  explosion  occur  in  the  blast  main  the  force  of  it  drives  back 
the  flap  on  to  its  seating,  thus  protecting  the  fan  from  damage,  and  expends  itself 
by  breaking  through  the  canvas  panels  of  the  box. 

It  is  customary  on  water-gas  plants  for  the  blower  engines  to  remain  running 


484 


MODERN   GASWORKS   PRACTICE 


Counterbalance 


Canvas  Panels 


at  full  speed  during  the  period  of  the 
"  run,"  when  they  are  performing  no 
useful  work.  Those  having  an  eye  to 
small  items  have  pointed  out  the 
wastefulness  of  such  procedure,  with 
the  result  that  in  some  instances  a  cut- 
out is  arranged  to  reduce  the  consump- 
tion of  steam  in  the  blower  engine 
while  the  run  is  proceeding.  The 
arrangement  may  be  easily  effected  in 
the  case  of  turbines,  but  it  presents  a 
greater  problem  with  reciprocating 
engines.  There  is,  moreover,  some 
question  as  to  its  advisability,  for  the 
amount  of  throttling  which  may  safely  be  practised  with  a  turbine  is  limited,  as 
the  latter  must  not  be  checked  so  that  its  critical  speed  be  passed.  In  addition, 
the  effect  of  the  air-blast  pressing  up  against  the  hot- gas  valve  during  the  "  run  " 
is  desirable,  in  that,  if  the  valve  is  not  perfectly  gastight,  gas  from  the  generator 


Canvas  Panels 


FIG.  331.— DETAIL  OF  FIG.  332. 


FIG.  332. — STEAM  TUKBINE  BLOWING  PLANT  FITTED  WITH  AUTOMATIC  SHUT-OFF. 

will  be  prevented  by  the  blast  pressure  (which  is  usually  greater  than  the  gas  pres- 
sure in  the  generator) '  from  leaking  back  into  the  blast  main,  although  such  an 
occurrence  is  unlikely  with  modern  valves  and  interlocking  gear. 


WATER   GAS  485 


In  order  to  ensure  the  effectual  and  economical  operation  of  a  water-gas  plant 
it  is  essential  that  frequent  attention  be  given  to  what  to  many  may  be  considered 
only  minor  features  of  the  process.  Exceptional  results,  however,  as  in  the  manu- 
facture of  coal  gas,  are  obtained  by  observing  the  utmost  care  in  connexion  with 
details  rather  than  by  concentrating  upon  the  more  apparent  items.  The  following 
may  be  considered  amongst  the  chief  factors  influencing  working  efficiency  : — 

(1)  The  Fuel  Bed.  In  the  single  generator  plant  {as  opposed  to  the  twin  variety) 
it  is  generally  laid  down  as  a  golden  working  rule  that  the  depth  of  the  fuel  bed 
must  always  be  maintained.  If  a  shallow  fuel  bed  is  .employed  it  cannot  be  dis- 
puted that  the  reduction  of  C02  to  CO  will  not  take  place  to  the  same  extent ;  hence 
the  final  product  will  contain  a  greater  proportion  of  the  former  gas.  At  the  present 
day,  however,  the  presence  of  a  small  extra  quantity  of  C02  is  more  or  less  im- 
material, and  the  author  has  no  hesitation  in  recommending  an  average  fuel  depth 
of  about  6  feet  6  inches.  By  working  at  this  level  the  period  of  blowing  may  be 
curtailed  (with  a  corresponding  gain  in  available  gasmaking  time),  and  the  capacity 
of  the  setting  will  be  appreciably  increased.  The  additional  amount  of  gas  obtained 
will  have  an  important  effect  in  reducing  cost  of  manufacture.  If  this  depth  of 
fuel  is  employed  the  coke  should  be  moderately  small,  nothing  greater  than 
3-inch  pieces  being  employed.  If  a  particularly  heavy  coke  is  made  use  of,  less  of 
it  will  be  required  as  compared  with  the  normal  gasworks  variety,  therefore  there 
need  be  no  hesitation  in  reducing  the  fuel  depth.  The  purity  of  the  coke  is  an  im- 
portant factor,  a  high  percentage  of  ash  causing  the  clinker  to  arch  over  and  hang 
up.  The  most  effective  remedy  for  troubles  of  the  kind  is  to  arrange  for  a  system 
of  periodical  "  down  runs."  In  this  way  the  clinker  is  driven  down  towards  the 
grate  bars  and  will  form  in  larger  pieces,  which  may  be  more  readily  dealt  with 
than  can  a  number  of  small  isolated  lumps.  A  "  down  run  "  should  be  arranged 
for  after  every  three  or  four  runs  in  the  upward  direction  ;  but  it  is  as  well  to  admit 
no  top  steam  for  at  least  an  hour  before  clinkering  takes  place.  As  regards  purity 
of  the  material,  it  may  be  noted  that  retort  carbon  makes  an  admirable  fuel  for  water 
gas  manufacture,  entirely  obviating  the  tedious  process  of  clinkering ;  but  its  com- 
mercial value  and  the  small  quantities  in  which  it  is  produced  on  gasworks  preclude 
the  possibility  of  its  use.  It  must  be  remembered  that  the  fuel  bed  and  the  fireclay 
walls  of  the  generator  are  the  stores  of  heat,  and  the  heat  retained  by  them  only  is 
available  for  the  reactions.  Temperatures  must  therefore  be  maintained,  the 
generator  being  worked  up  to  at  least  2,000°  Fahr.  before  the  "  run  "  is  commenced. 
By  the  time  the  run  is  completed  the  temperature  will  have  dropped  some  300°  to 
500°  Fahr.  The  effect  of  this  is  shown  by  the  manner  in  which  the  make  of  gas 
falls  off  towards  the  end  of  the  run,  with  a  gradual  increase  in  the  C02  content. 
Stelfox,  experimenting  with  seven-minute  and  eight-minute  "  runs,"  found  the 
following  results  : — 


486 


MODERN   GASWORKS   PRACTICE 


SEVEN-MINUTE  "RUN." 

ElGHT-MlNUTE    "RUN." 

Gas  made  during  1st  minute  

1,882  cubic  feet 

1,840  cubic  feet 

2nd       „       
„       3rd        „       ...... 
„       4th        „       

1,554 
1,472 
1,472           „ 

1,595 
1,513 
1  308 

„       5th        ,,       

1,144 

1,103           „ 

»       6th        ,  
„       7th       „       ...... 
„       8th        ,,       

982 
492 

941 
410 
410 

Total  

8  998           „ 

9,120             , 

As  regards  the  rate  of  increase  of  the  C02  content  the  author  finds  that,  work- 
ing under  the  conditions  of  a  comparatively  shallow  fuel  bed  as  suggested  above,, 
the  following  may  be  taken  as  an  average  example  with  a  six-minute  "  run  "  : — 


GENERATOR  GAS. 

Percentage  of  CO2. 

Percentage  of  CO. 

End  of  1st  minute   
„     2nd      „         ......... 
„     3rd      „         

2-2 
3-6 
4-3 

5-8 
7-9 
9-4 

46-3 
42-0 
40-1 
33-6 
31-9 
28-4 

„     4th      „         

„     5th      ,  
„     6th      „         

The  policy  of  superheating  the  steam  before  its  admission  to  the  generator 
is  one  on  which  much  discussion  has  taken  place.  Certainly,  by  this  means  a  greater 
store  of  heat  is  ensured  in  the  generator,  and  superheating  is  provided  for  in  the 
Dellwik  and  some  "  K.  &  A."  plants.  If  the  practice  can  be  carried  out  without 
introducing  structural  complications,  and  by  making  use  of  heat  which  would  other- 
wise be  wasted,  it  is,  no  doubt,  to  be  commended.  But  in  any  case  the  effect  will 
be  limited.  Glasgow  has  pointed  out  that  even  when  superheated  to  1,5CO°  Fahr. 
the  stearn  carries  scarcely  9,000  additional  heat  units,  or  but  2i  per  cent,  of  the 
energy  absorbed  in  the  manufacture  of  the  carburetted  product.  The  provision 
of  a  dry  steam  is,  however,  essential ;  and  to  this  end  the  boilers  should  be  adjacent 
to  the  plant,  the  steam  mains  being  adequately  lagged,  and,  if  necessary,  trapped. 
Sufficient  and  uniform  boiler  pressure  is  essential,  for  if  the  steam  pressure  is  per- 
mitted to  fluctuate  to  any  marked  extent  it  will  be  followed  by  disastrous  results 
on  the  output  of  the  plant.  Many  installations  are  designed  to  operate  with  steam 
at  130  Ib.  per  square  inch,  though  100  Ib.  pressure  is,  perhaps,  more  common.  In  the 
latter  case,  some  appreciable  improvement  will  frequently  be  followed  by  increasing 


WATER   GAS 


487 


the  pressure  to  110  lb.,  if  the  boilers  are  capable  of  taking  the  increase.  Steam 
meters  are -an  undoubted  asset  to  any  plant,  and  enable  accurate  adjustment  to 
be  made.  The  factor  of  the  quantity  of  steam  admitted  is  of  greater  importance 
than  might  at  first  sight  be  supposed.  Whilst  a  sufficiency  of  steam  is  imperative, 
an  excess  is  to  be  rigidly  avoided.  If  too  great  a  quantity  is  admitted  the  surplus 
steam  passing  through  the  fuel  bed  may  actually  account  for  a  reduction  in  the 
quantity  of  CO,  with  a  corresponding  increase  in  C02,  thus  : — 

H20  +  C0  =  C02+H2. 

—a  reaction  which  may  occur  tolerably  easily  at  present-day  generator  temperatures 
of  2,000°  Fahr.  In  general,  it  will  be  found  that  for  effective  results  the  consumption 
of  steam  will  amount  to  from  27  to  30  lb.  per  1,000  cubic  feet  of  gas.  Thus,  with 


FIG.  333. — DIAGRAM  SHOWING  PRINCIPLE  OF  STEAM  METER. 

a  plant  making  8,000  cubic  feet  per  run  of  five  minutes  the  steam  should  be  set  at 
a  rate  of  about  45  lb.  per  minute.  It  will  be  found  that  the  "  down  run  "  supply 
can  be  adjusted  to  give  a  rather  greater  flow  than  the  up  steam,  roughly  about  2  ,lb. 
per  minute  more. 

Steam  meters,  as  used  on  water-gas  plants,  are  calibrated  to  read  pounds  of 
steam  passing  per  minute.  There  are  many  types,  most  of  which  are  constructed 
to  read  direct  on  a  dial,  or  to  give  an  autographic  record.  Kent's  steam  meter 
(Fig.  333)  is  based  upon  the  principle  that  steam  flowing  through  a  constriction  in 
a  pipe  falls  in  pressure,  the  pressure  drop  being  approximately  proportional  to 
the  square  of  the  velocity  of  flow.  The  constriction  consists  of  an  orifice  plate 
which  is  bolted  between  two  flanges,  the  size  of  the  orifice  being  such  that  the  desired 
pressure  drop  at  the  maximum  discharge  is  obtained.  The  pressures  from  the  inlet 


MODERN   GASWORKS   PRACTICE 


and  outlet  sides  of  the  orifice  are  conveyed  through  copper  pipes  to  the  two  portions 
of  the  diaphragm,  the  movement  of  which  corresponds  to  the  differential  pressure 
created  by  the  steam  flow.  The  diaphragm  movement  is  then  transmitted  through 
a  gland  to  the  indicating  mechanism.  The  loss  of  pressure  due  to  the  insertion  of 
the  orifice  amounts  to  about  £  Ib.  per  square  inch  at  maximum  flow. 

;(2)  The  Blow.  The  direction  of  the  blast  is  always  upward,  no  reversal  being 
possible  as  in  the  case  of  the  steam.  The  pressure  of  the  air  as  delivered  from  the 
fan  usually  varies  between  17  inches  and  22  inches  of  water,  but  much  depends 
upon  the  type  and  size  of  the  plant  and  the  fan  capacity  available.  It  must  be 
'borne  in  mind,  however,  that  the  blast  must  under  all  circumstances  provide  an 
•excess  of  air,  otherwise  the  extent  to  which  combustion  to  C02  takes  place  will 
ibe  limited,  with  the  result  that  less  heat  is  dispersed.  It  will  be  remembered,  in  this 
connexion,  that  the  partial  combustion  of  coke  to  CO  accounts  for  only  one-third 
of  the  heat  derived  from  complete  combustion  (see  page  48). 

As  is  to  be  expected,  the  construction  of  blowing  fans  has  undergone  some 
considerable  modification  since  the  introduction  of  water  gas. 

Some  twenty  or  more  years  ago,  when  the  manufacture  of  water  gas  was  in  its 
infancy,  a  blast  pressure  of  from  8-inch  to  15-inch  water-gauge  wras  considered 
suitable  for  the  generators,  and  any  good  blowing  fan  would  do  the  work. 

A  few  years  later  the  output  of  gas  plants  was  largely  increased  by  running  the 
fans  at  greater  pressures,  and,  as  the  speeds  required  for  the  new  conditions  were 
too  high  for  the  fans  then  in  use,  the  results  in  many  cases  were  disastrous.  In  order 
to  meet  the  conditions  a  special  extra  heavy  fan  was  then  introduced.  This  new 
-type  of  fan,  made  exclusively  for  water-gas  purposes,  is  capable  of  supplying  air  at 
a  pressure  of  from  15-inch  to  25-inch  water-gauge,  or  even  greater  pressures 
if  necessary. 

Bearing  in  mind  the  very  important  duty  performed  by  the  blowing  fan  in  the 
manufacture  of  water  gas,  it  cannot  be  emphasized  too  strongly  that,  in  order  to 
•eliminate  as  far  as  possible  all  risk  of  breakdown,  the  blowing  apparatus  should 
foe  specially  designed  and  suitable  for  long  runs  with  a  minimum  of  attention. 

The  following  table  gives  the  approximate  size  of  fan  (Sturtevant  type)  required 
for  a  given  size  of  water-gas  plant  : — 


Standard  Size 
of  Fan. 

Capacity  of  Water-Gas 
Plant.     Cubic    feet    per 
diem. 

B.H.P. 
absorbed  by  Fan. 

Speed  of  Fan. 
Revs,  per  minute. 

4 

150,000 

10-25 

3,400 

5 

200,000 

14-50 

2,920 

6 

300,000 

15-50 

2,475 

7 

500,000 

23-50 

2,175 

8 

650,000 

32 

1,625 

9 

850,000 

44 

1,425 

10       * 

1,000,000 

58 

1,225 

In  view  of  the  fact  that  fans  operating  in  conjunction  with  water-gas  plants 


WATER   GAS 


489 


have  to  work  intermittently,  it  would  not  seem  advisable  to  employ  blowers 
of  the  positive  type.  For  instance,  when  no  blast  is  required  a  positive  blower  must 
be  stopped  altogether,  or  a  valve  must  be  fitted  on  the  blast  main  to  release  the  air 
when  the  pressure  rises  above  a  pre-determined  figure.  The  latter,  however,  is 
a  somewhat  wasteful  proposition.  With  this  type  of  blower,  moreover,  the  ques- 
tions of  wear  and  tear  and  noise  during  working  have  to  be  considered.  With*  a 
centrifugal  fan  it  is  possible  to  regulate  the  delivery  of  air  by  a  valve  placed  in 
the  blast  main,  the  speed  of 
the  fan  being  kept  constant. 
As  the  valve  is  closed  or 
opened,  less  or  more  air  is 
allowed  to  pass  to  the  genera- 
tor, and  the  power  absorbed 
by  the  fan  rises  or  falls  accord- 
ing to  whether  the  valve  is 
opened  or  closed. 

(3)  Amount  of  Air  re- 
quired. The  amount  of  air 
which  should  be  required  dur- 
ing the  period  of  the  "  blow  " 
is  most  readily  gauged  upon 
the  gas-producing  capacity  of 
the  plant.  As  a  general  rule 
it  may  be  taken  that  the 
quantity  of  air  should  not 
exceed  from  2,000  to  2,500 
cubic  feet  per  1,000  cubic  feet 
of  gas  made.  Thus,  with  a 
medium-sized  plant,  making 
8,000  cubic  feet  during  a  five- 
minutes'  "  run,"  the  total  air 
passed  should  lie  between  4,000 
and  5,000  cubic  feet  per 
minute.  It  has  been  pre- 
viously pointed  out  that  as  the 
"  blow  "  proceeds,  so  does  the 
proportion  of  carbon  monoxide 
in  the  producer  gas  increase. 
For  this  reason  it  has  been 

suggested  that  the  fan  should  be  gradually  speeded  up  so  that  a  greater  volume 
of  air  is  passed  towards  the  end  of  the  "  blow."  The  practice  has,  as  a  matter  of 
fact,  been  tried,  but  general  experience  has  gone  to  show  that  the  benefits  are  not 
commensurate  with  the  additional  complications  entailed.  A  more  satisfactory 
arrangement,  from  the  practical  point  of  view,  is  that  of  gradually  increasing  the 


FIG.  334. — AIR  METER  ATTACHED  TO  GENERATOR  BLAST 
MAIN. 


490  MODERN   GASWORKS   PRACTICE 

secondary  air  to  the  carburettor  and  superheater  during  the  "blow."  This  can 
be  conveniently  done  in  a  hydraulically  operated  plant  such  as  that  at  the  Beckton 
works.  Air  meters  fitted  to  the  blast  main  are  more  or  less  a  luxury,  but  are  occa- 
sionally found.  Fig.  334  shows  an  air  meter  of  the  Venturi  type. 

The  satisfactory  regulation  of  the  blast  is  a  considerable  factor  in  water-gas 
operation,  for  it  must  be  remembered  that  very  much  more  fuel  may  be  consumed 
during  the  "  blow  "  than  is  actually  made  use  of  for  gasmaking.  With  extravagantly 
operated  plants,  in  which  the  blast  may  be  excessive,  the  fuel  burnt  during  the 
"  blow  "  may  amount  to  three  or  even  four  times  the  quantity  disposed  of  during 
the  "  run."  A.  G.  Glasgow  in  a  test  with  a  plant  consuming  hard  coal  found  that, 
working  under  favourable  conditions,  the  consumption  of  carbon  during  "  blow  " 
and  "  run  "  was  as  13'88  to  9'62,  or,  about  60  per  cent,  was  accounted  for  during 
the  "  blow,"  and  40  per  cent,  was  used  for  gasmaking. 

For  effective  results  it  is  essential  that  local  blowing,  or  imperfect  distribution 
of  the  air  blast  and  the  steam  supply,  should  be  avoided.  For  this  reason  the  fuel 
supplied  to  the  generator  should  be  as  uniform  in  size  as  possible.  If  clinkering 
is  imperfectly  carried  out  and  large  lumps  are  allowed  to  form  and  remain  lodged 
up  in  the  generator  effective  distribution  is  impossible.  Thus  the  air  blast  will 
find  its  way  through  certain  portions  only  of  the  bed,  which  portions  will  be  raised 
to  an  abnormally  high  temperature,  whilst  the  remainder  of  the  bed  is  in  a  con- 
dition of  comparative  coolness.  Local  steaming  of  the  bed  may,  in  the  same  way, 
be  due  to  the  formation  of  clinker,  although  it  frequently  occurs  from  the  steam 
supply  nozzle  being  non-central,  partly  choked,  or  broken. 

Owing  to  the  gradual  reduction  in  temperature  of  the  fuel  bed  during  the  "  run  " 
it  has  been  suggested  that  the  steam  supply  should  undergo  reduction  as  the  period 
of  gasmaking  proceeds.  In  this  way  a  rather  better  quality  gas  will  be  obtained, 
but  the  capacity  of  the  plant  is  to  a  certain  extent  curtailed.  The  gradual  diminu- 
tion of  the  steam  is,  therefore,  the  exception  rather  than  the  rule. 

(4)  Periods  of  "  Run  "  and  "  Blow."  The  duration  of  the  "  run  "  and  "  blow  " 
differs  in  accordance  with  the  type  of  plant.  The  following  show  the  average 
conditions  of  working  : — 

"  RUN."  "  BLOW." 

Lowe  Plant          .          .         ..         .         .         .     .    «     5  minutes  and     3  minutes. 

or         6  minutes  and    4  minutes. 
"  K.  &  A."  Plant        .          .          .          .  -     ..,-         .5  minutes  and  70  seconds. 

Dellwik  Plant      .          .          .         .          .          .          .6  minutes  and  60  seconds. 

With  the  standard  type  of  carburetting  plant  the  author  has  found  that  the 
most  favourable  results  are  obtained  by  working  on  the  five- minutes'  "  run  "  and 
three-minutes'  "  blow  "  cycle,  but  that  the  "  run  "  immediately  prior  to  recharging 
the  generator  may  be  prolonged  to  six  minutes.  At  such  stages  the  fire  is  shallow 
and  exceedingly  hot,  and  there  appears  to  be  a  good  yield  of  gas  during  the  extra 
minute.  After  coking  up,  moreover,  it  is  as  well  to  prolong  the  "  blow  "  to  four 
minutes. 

Clinkering  on  water-gas  plants  must  be  carried  out  at  frequent  intervals,  for 


WATER   GAS 


491 


if  once  the  mass  is  allowed  to  grow  it  will  gradually  arch  over  in  the  generator  until 
the  latter  is  almost  completely  choked.  With  the  Lowe  plants  it  is  advisable  to 
perform  the  operation  at  intervals  of  four  hours,  although  in  cases  where  a  good 
quality  coke  is  procurable  the  period  may  be  prolonged  to  six  hours.  In  many 
of  the  "  blue  "  gas  plants  with  double  generators  clinkering  takes  place  only  once 
in  ten  or  twelve  hours.  In  recent  years  mechanical  grates,  which  obviate  the  greater 
portion  of  the  labour  entailed  in  clinkering,  have  been  introduced,  but  they  are  as 
yet  confined  to  generators  of  the  larger  capacities.  Briefly,  they  consist  of  specially 
designed  firebars  which  are  caused  to  rotate  and  scrape  out  both  clinker  and  ashes. 
A  generator  fitted  with  such  a  grate,  designed  by  Humphreys  and  Glasgow,  is  seen 


FIG.  335. — GENERATOR  FITTED  WITH  AUTOMATIC  CLINKERING  DEVICE. 

in  Fig.  335.     The  Kerpely  producer,  which  is  built  with  a  specially  revolving  ash- 
extracting  grate,  has  already  been  referred  to  in  Chapter  III  (see  page  81). 

(5)  Carburation.  In  the  original  plants  employed  for  the  manufacture  of  car- 
buretted  water  gas  it  was  usual  to  spray  the  oil  direct  on  to  the  fuel  in  the  generator. 
This  procedure,  however,  proved  decidedly  wasteful,  with  the  result  that  a  separate 
vessel  was  soon  introduced  for  purposes  of  carburation.  The  duty  obtained  from 
the  carburetting  medium  employed  will  largely  depend  upon  the  manner  in  which 
the  vessel  is  operated  and  maintained,  whilst  temperature  is  a  factor  of  considerable 
importance.  The  main  consideration  to  bear  in  mind  is  that  the  heat  must  be  sum- 


492  MODERN   GASWORKS   PRACTICE 

cient  to  crack  up  the  oil  into  vapours  which  will  as  far  as  possible  be  retained  as 
permanent  gases,  but  it  must  not  be  so  great  as  to  cause  such  degradation  as  gives 
rise  to  over-cracking  and  the  deposition  of  free  carbon.  Frequently,  it  is  stated 
that  a  desirable  working  temperature  for  both  carburettor  and  superheater  is  1,7CO° 
Fahr.,  or  thereabouts.  The  author  finds,  however,  that  for  high  results  in  the 
direction  of  "  candles  per  gallon  "  the  American  oil  as  now  almost  universally  used 
is  preferably  decomposed  at  lower  temperatures.  Moreover,  it  will  be  found  advan- 
tageous to  work  the  superheater  at  slightly  higher  temperatures  than  the  carburettor. 
The  temperatures  suggested  when  under  normal  working  conditions  are  : — 

Carburettor        .          .          .          .          .     between  1,350°  and  1,400°  Fahr. 
Superheater       .....          .          .  „         1,400°  and  1,450° 

This,  however,  must  not  be  considered  as  a  hard-and-fast  rule,  for  very  much 
•depends  upon  the  quantity  of  oil  being  injected  during  the  "  run."  For  instance, 
if  a  poorer  quality  gas  is  being  manufactured,  and  only  about  half  the  normal  quan- 
tity of  oil  is  in  use,  the  temperature  must  be  regulated  in  accordance.  Another 
factor  is  the  time  taken  to  inject  the  oil.  The  quantity  sprayed  in  must  not  be  so 
apportioned  that  oil  is  running  in  during  the  whole  of  the  gasmaking  period.  Such 
procedure  would  lead  to  inevitable  waste,  for  the  carburettor  and  superheater  would 
not  be  swept  clean  from  oily  matter  before  the  commencement  of  the  "  blow." 
Generally,  it  may  be  said  that  it  is  as  well  to  arrange  for  the  desired  quantity  of 
oil  to  be  sprayed  in  during  the  first  half  of  the  "  run  "  or  thereabouts.  For  instance, 
with  a  five-minutes'  "  run  "  the  oil  may  be  got  rid  of  in  the  first  three  minutes,  leaving 
two  minutes  for  the  manufacture  of  "  blue  "  gas,  which  will  perform  the  necessary 
scavenging  of  the  remaining  vessels.  The  oil  spray  is  a  matter  of  importance,  and 
thorough  atomization  should  be  aimed  at.  It  would  seem  that  rather  than  the  oil 
should  be  injected  under  a  pressure  of  40  Ib.  per  square  inch  it  is  preferable  to  employ 
higher  pressures  of  from  80  to  ICO  Ib.  Such  pressure  in  conjunction  with  a  spray 
of  the  Brighton  type  (Fig.  336)  gives  the  most  effective  mechanical  subdivision  and 
uniform  distribution.  The  extremely  fine  distribution  of  the  oil  in  this  manner 
tends  towards  maintaining  the  chequer- work  of  the  carburettor  in  a  more  cleanly 
condition,  whilst  patchiness  in  heating  is  avoided.  It  is  customary  on  gasworks 
in  arriving  at  an  indication  of  the  efficiency  obtained  from  the  oil  to  note  from  day 
to  day  the  yield  of  "  candles  per  gallon."  This  figure  is  arrived  at  by  taking  the 
average  candle  power  of  the  gas  and  dividing  it  by  the  oil  used  per  1,000  cubic  feet 
of  gas  made  over  the  same  period.  In  practice  the  result  varies  between  7  and  8 
;candles  per  gallon,  but  the  latter  figure  should  be  easily  obtainable  when  the  set  is 
worked  on  effective  lines.  It  may  be  stated  here  that  the  amount  of  gas  yielded 
per  gallon  of  American  gas  oil  varies  from  70  to  90  cubic  feet. 

A  rough-and-ready  test  which  may  be  applied  to  the  superheater  in  order  to 
determine  whether  the  most  is  being  made  of  the  oil  is  merely  that  of  holding,  during 
the  "  run,"  a  piece  of  clean  blotting  paper  to  a  small  jet  of  the  gas  taken  off  from  the 
down  pipe  from  the  superheater.  If  the  oil  is  being  subjected  to  too  great  a  heat 
a  small  black  deposit  of  free  carbon  will  be  found  on  the  paper ;  if,  on  the  other 
hand,  it  is  insufficiently  cracked,  a  slight  deposit  of  an  oily  nature  will  result.  In 


WATER   GAS 


493 


the  majority  of  carburetting  plants  a  device  is  in  use  whereby  the  oil,  before  being; 
passed  into  the  carburettor,  is  preheated  by  the  hot  gas  leaving  the  plant.  The 
heater  is  usually  placed  in  the  down  pipe  leading  from  the  superheater,  and  raises 
the  temperature  of  the  oil  to  about  230°  Fahr.  In  this  way  the  "  candles  per 
gallon  "  are  appreciably  enhanced ;  but  the  author  would  point  out  that  in  some 
instances  he  has  found  that  the  removal  of  the  oil  heater  has  been  followed  by  a 
general  improvement  in  results.  This  fact  is  ascribed  to  the  reason  that  the  heater 
appropriates  a  considerable  portion  of  the  area  of  the  main  gas  outlet,  with  the 
result  that  the  latter  is  insufficiently  large  for  the  gas  to  get  away  with  the  ease  it 


FIG.  336. — DETAILS  OF  "  BRIGHTON  "  OIL  SPRAY. 

should  do.  A  point  which  is  patent  to  all  users  of  water-gas  plant  is  the  necessity 
for  scavenging  the  apparatus  prior  to  commencing  the  "  blow."  When  the  steam 
is  shut  off  at  the  end  of  the  "  run  "  the  vessels,  the  cubic  capacity  of  which  is  fairly 
considerable,  remain  full  of  water  gas.  To  open  the  stack  valve  at  once  and  to  com- 
mence with  the  "  blow  "  would  be  to  discharge  this  water  gas  into  the  air.  To  pre- 
clude this,  after  the  steam  is  shut  off  the  stack  valve  should  remain  closed,  not 
being  opened  until  the  air  blast  has  been  passing  through  for  a  few  seconds.  In 
this  way,  the  gas  will  be  driven  forward  to  the  holder,  and  the  plant  will  be  effectively 
cleared  out. 

MATERIALS  USED 

The  materials  used  for  the  manufacture  of  carburetted  water  gas  vary,  as  regards 
quantity,  between  the  following  limits  : — 

Coke      .         .         .32  to  41  Ib.  per  1,000  cubic  feet  of  gas. 

Oil      ...      .          .     about  2J  gallons  per  1,000  cubic  feet  of  18  candle  power  gas. 

Steam    .          .          .     27  to  30  Ib.  per  1,000  cubic  feet  of  gas. 

A  figure  of  35  Ib.  for  coke  consumption  is  probably  the  most  favourable  ob- 
tained with  plants  of  the  Lowe  type,  but  some  reduction  on  this  may  foe  expected 
in  those  cases  where  the  pan  coke  is  extracted  from  the  generator  refuse  and  deducted 
from  the  total  weight  of  coke  shot  into  the  generator.  Plants  designed  essentially  for 
the  production  of  "  blue  "  gas  are  generally  able  to  economize  in  the  direction  of 
fuel,  and  figures  so  low  as  25  Ib.  of  coke  per  1,000  cubic  feet  have  been  obtained. 
As  an  average,  however,  the  quantity  will  vary  between  30  and  34  Ib.  These  figures, 
as  in  the  case  of  those  given  for  carburetting  plants,  are  exclusive  of  the  fuel  required 


494  MODERN   GASWORKS    PRACTICE 

in  the  boilers  for  steam  raising.  The  steam-raising  plant  will,  with  the  mixture  of 
breeze  and  coke  usually  employed  on  gasworks,  require  an  additional  12  to  15  Ib.  of 
fuel  per  1,COO  cubic  feet  of  gas  made. 

The  cost  of  manufacture  of  water  gas  must  depend  largely  upon  the  current 
market  values  of  the  raw  products,  coke  and  oil,  the  latter  accounting  for  from 
50  to  65  per  cent,  of  the  whole.  For  this  reason  it  will  be  seen  that  the  manufacture 
of  "  blue  "  gas  is  a  very  much  less  costly  undertaking  than  is  the  case  with  a 
carburetted  gas.  In  general,  the  following  statement  will  conform  to  normal 
conditions  : — 

18  CANDLE  POWER  CARBURETTED  GAS. 

Coke  for  generators       .          .          .  .  4d.  per  1,000  cubic  feet  of  gas. 

Coke  for  steam  raising.          .  .  .        .  lie?.        ,,  „  ,, 

Oil,  2£  gallons  at  4rf 9d. 

Wages. Hrf.        „  „  „ 

Wear  and  Tear     .  Id. 


Is.  5d. 
Less  Residuals  — 

Tar  .          .          .          .         .  0-M. 

Pan  coke.          .          .          .          .  0-07c?. 

Sulphur     ...          .          .          .  0-03d. 


Net  cost  Is.  4-3d.  per  1,000  cubic  feet. 

The  above  represents  the  case  for  a  medium-sized  plant.  It  will,  of  course, 
be  quite  evident  that  as  the  size  of  the  unit  increases  so  do  the  various  individual 
items  undergo  reduction,  for  the  gas-producing  capacity  of  the  attendant  and 
general  working  efficiency  are  enhanced  pro  rata.  The  above  example  illustrates 
in  a  marked  degree  the  influence  of  the  current  value  of  oil  on  the  cost  of  the  gas. 
At  one  time  oil  could  be  obtained  for  somewhat  less  than  Id.  per  gallon,  but  the 
extent  to  which  it  is  likely  to  fluctuate  is  emphasized  by  the  fact  that  during  the 
European  war  large  consumers  were  obliged  to  pay  nearly  IQd.  As  regards  capital 
cost,  much  again  depends  on  the  size  of  the  installation  ;  but  in  normal  times  it 
may  be  assumed  for  a  complete  plant  of  the  Lowe  type,  including  housing,  boilers, 
exhausters,  purifiers,  relief  holder,  etc.,  to  lie  between  £20  and  £25  per  1,000  cubic 
feet  of  capacity.  The  approximate  cost  of  the  various  portions  of  the  apparatus  is 
exemplified  in  the  instance  given  in  Chapter  I,  page  25. 

THE  COMPOSITION  OF  WATER  GAS 

With  the  exception  of  the  diluents  nitrogen  and  carbon  dioxide,  straight  or  "blue" 
water  gas  consists  almost  solely  of  hydrogen  and  carbon  monoxide.  A  small  per- 
centage of  methane  is  usually,  but  not  necessarily,  present.  The  final  composition 
of  carburetted  water  gas  necessarily  depends  to  a  large  extent  upon  the  proportion 
of  oil  used  in  its  manufacture.  Under  any  circumstances,  the  constituents  differ 
to  some  considerable  extent  from  those  of  coal  gas.  As  regards  hydrocarbons, 


WATER   GAS  495 

those  of  the  unsaturated  variety  absorbed  by  bromine  will  be  present  to  the  extent 
of  about  10  per  cent,  in  a  gas  of  18  candle  power.  The  same  quality  gas  will  also 
contain  about  13  per  cent,  of  paraffins,  the  greater  portion  of  which  will  consist 
of  methane.  The  unsaturated  hydrocarbons,  with  present-day  heats,  consist 
largely  of  the  benzene  series. 

As  regards  the  mixture  of  coal  gas  and  carburetted  water  gas  as  supplied  to 
consumers,  with  the  usual  proportion  of  carburetted  gas,  that  is  from  25  to  30  per 
cent,  by  volume,  having  an  illuminating  power  of  from  17  to  18  candles,  and  admixed 
with  coal  gas  of  from  13  to  13£  candles,  the  composition  of  the  mixture  will 
approach  'the  following  : — 

COMPOSITION  OF  MIXED  GAS,  ABOUT  14 \  CANDLE  POWER. 

Hydrogen     .          .          .          .          .       -  .          .          .44-0  per  cent,  by  volume. 

Methane ,-        .          .     22-0 

Unsaturated  hydrocarbons     .          .         ...          .       5-8          ,,  „ 

Carbon  monoxide.          .          .          .         .          .          .     16-5          „  „ 

Carbon  dioxide    ..          .          .          .          .          .          .  ,    3-5          ,,  „ 

Nitrogen       ........       8-2         „  „ 

In  addition  to  the  above  there  might  be  found  an  amount  of  oxygen  varying 
from  traces  to  0'2  per  cent. 

When  used  for  the  purpose  of  enriching  a  coal  gas  of  low  quality,  carburetted 
water  gas  appears  to  possess  the  property  of  enhancing  the  illuminating  power  of 
the  mixture  to  a  greater  extent  than  is  shown  by  theoretical  reckoning.  For  in- 
stance, if  75  per  cent,  of  the  mixture  consists  of  coal  gas  of  13  candles  and  25  per 
cent,  is  made  up  from  water  gas  of  18  candles,  the  final  candle  power  obtained 
should,  by  computation,  be  14-25.  In  practice,  however,the  actual  candle  power  of  the 
mixture  will  be  in  the  neighbourhood  of  15  candles,  thus  showing  the  additional 
enriching  effect  obtained.  The  explanation,  no  doubt,  is  one  of  flame  temperature, 
water  gas  burning  with  a  smaller  flame  than  coal  gas  ;  and,  when  admixed  with  the 
latter,  the  carbon  particles  of  the  coal  gas  are  raised  to  a  higher  degree  of  luminosity 
than  when  the  coal  gas  is  burned  bv  itself. 

o  •/ 

The  impurities  in  water  gas  consist  of  sulphuretted  hydrogen  and  carbon  disul- 
phide.  The  gas  is  generally  free  from  ammonia,  but  occasional  traces  of  this 
may  be  founc^.  The  proportions  in  which  the  impurities  are  present  are  approxi- 
mately as  follows  : — 

Sulphuretted  hydrogen         .          .          .         .  110  to  120  grains  per  100  cubic    feet,    or 

about  0-2  per  cent,  by  volume. 
Carbon  disulphide  and  other  sulphur  compounds       .     10  to  15  grains  per  100  cubic  feet. 

The  specific  gravity  of  water  gas  is  higher  than  that  of  coal  gas,  the  gravity 
of  the  carburetted  gas  being  in  the  neighbourhood  of  0-65  as  against  an  average 
figure  of  047  for  coal  gas. 

The  manner  in  which  the  specific  gravity  of  water  gas  increases  with  the  candle 
power  is  shown  by  the  following  results  obtained  by  F.  H.  Shelton  : — 


496 


MODERN   GASWORKS   PRACTICE 


CANDLE  POWER. 
19-5 
20-0 
22-5 
24-0 
254 
26-3 
28-3 
29-6 
30  to  31-9 


SPECIFIC  GRAVITY  (Air  =  l). 

0-571 

0-630 

0-589 
0-60  to  0-67 

0-64 

0-602 

0-70 

0-65 
0-65  to  0-71 


COMPOSITION  OF  VARIOUS  GASES 


Coal  Gas. 

Carbur- 
etted 
Water 

"  Blue  " 
Water 
Gas. 

Mond  Gas 

Suction 
Gas. 

Dowson 
Gas. 

Gas. 

Per  cent. 

Per  csnt. 

Hydrogen                  .... 

49 

35-0 

52-0 

26-0 

16-0 

20-0 

Carbon  monoxide     .... 

9 

32-0 

38-0 

15-0 

34-0 

24-0 

Carbon  dioxide   

3-5 

4-5     ' 

4-5 

12-0 

3-0 

6-0 

Methane   

27-0 

13-0 

J-0 

3-0 

nil 

1-0 

Heavy  hydrocarbons  (CnHm). 

4-0 

10-0 

nil 

nil 

nil 

nil 

Nitrogen  

7-5 

5-5 

4-5 

44-0 

47-0 

49-0 

Candle  power      

14-0 

18 

nil 

nil 

nil 

nil 

Calorific  power  gross.   B.Th.U. 

per  cubic  foot     .... 

550 

580 

300 

165 

160 

155 

WATER-GAS  TAR 

The  quantity  of  tar  thrown  down  during  the  scrubbing  and  condensation  o£ 
carburetted  water  gas  will  amount  to  from  12  to  16  gallons  per  100  gallons  of  oil 
gasified.  This  tar  is,  unfortunately,  a  frequent  source  of  trouble  in  two  directions. 
First,  the  lighter  tarry  vesicles  which  are  difficult  to  remove  from  the  gas  in  the 
preliminary  stages  remain  suspended  therein  and  are  eventually  extracted  as  the 
gas  passes  through  the  oxide  purifiers.  The  tar,  being  deposited  on  the  oxide,  not 
only  reduces  its  activity  and  gives  rise  to  excessive  back-pressure,  but  it  renders  the 
spent  material  of  little  commercial  value.  Many  mechanical  devices  have  been 
employed  with  a  view  to  removing  the  suspended  particles  of  tar  before  the  gas 
arrives  at  the  dry  purification  plant.  One  of  the  most  successful  di:  these  is  the 
"  Hurricane  "  trap  shown  in  Fig.  337,  which  is  fitted  in  a  vertical  main  where  the 
flow  of  gas  is  downwards.  The  apparatus  consists  of  a  cone  A,  having  its  apex 
against  the  flow  of  gas  and  its  base  formed  into  a  ring  plate  B  about  6  inches  in 
depth.  An  annular  space  is  formed  around  the  ring  plate  by  fixing  a  second  ring, 
C,  mounted  on  a  foundation  plate,  D,  the  other  end  of  which,  E,  forms  another 
ring.  A  second  cone,  F,  is  suspended  below  the  upper  one,  the  diameter  of  this  cone 
being  some  3  inches  less  than  that  of  the  main.  The  gas  to  be  treated  is  obliged 
to  pass  through  the  narrow  annular  space,  where  it  is  wire-drawn,  the  vesicles  being 
made  to  agglomerate  and  form  a  rain.  The  gas  is  then  deflected  upwards  on  to  the 


WATER   GAS 


497 


FIG.  337. — "  HURRICANE  "  TAB  EXTRACTOR. 


underside  of  the  top  cone,  which  again  deflects  it  downwards  on  to  the  top  of  the 
lower  cone.     This  lower  cone  receives  the  deposit  of  tar  rain,  which  trickles  from  the 
edges  and  runs  away  to  the  seal. 

There  is  no  doubt  that  wire-drawing,  if  effectively  carried  out,  can  be  used 
successfully  for  the  removal  of  tarry  vesicles.     It  would  appear,  however,  that  the 
principle  of  bubbling  as  embodied  in 
washers  of  the  Livesey  type  is  diffi- 
cult to  improve  upon.     A  washer  of 
this  description  (into  which   a  small 
stream  of  liquor  from  the  water  gas 
scrubber  is  constantly  permitted  to 
run),  fitted  prior  to  the  carburetted 
water-gas  purifiers,  will  usually  elimin- 
ate  almost  the   whole   of    the    sus- 
pended particles  in  the  gas.     It  must 
not    be     forgotten,    moreover,    that 
efficient  condensation  is  an  import- 
ant item  in  this  respect,  and  if  the 
gas  is  permitted  to  leave   the   condensers  at  an  abnormally  high   temperature, 
trouble  is  only  to  be  expected. 

In  the  second  direction  water-gas  tar  is  in  many  cases  an  annoyance  in  that, 
being  of  practically  the  same  specific  gravity  as  water,  it  admixes  with  the  latter 
and  forms  an  emulsion  of  a  very  permanent  character.     The  consequence  is  that 
the  tar  as  made  ready  for  sale  may  contain  so  much  as  40  per  cent,  of  water.     Various 
means,   including  centrifugal  treatment,   heating,   etc.,  have  been  experimented 
with  for  the  purpose  of  effecting  separation,  but  the  matter  still  remains  something 
of  a  problem. 

As  regards  the  composition  of  tar  from  the  manufacture  of  carburetted  water 
gas,  S.  Carter  has  given  the  following  analysis  : — 
Specific  gravity,  1-0665. 
Benzol,  90  per  cent.          „         .         .          .          .'         .       1-11  per  cent. 

Naphtha.          .          .          .  '       .          .          .          .          .       2-33        „ 

Creosote  oil      .  .         .          .          .          .          .     21-35        „ 

Naphthalene     .          .          .         .         .    '  .  .       J       4-09       „ 

Anthracene  oil  .         ......          .     15-91        „ 

Pitch     .  .          .          .         .         ;"       .          .-        .     56-70 

For  the  same  type  of  tar  Matthews  and  Goulden  give  the  following  figures  : — 
Benzene  .          .  .          .          .          .        '.       1-19  per  cent. 

Toluene ;  .     '     .          .'     0-83          „ 

Paraffins.          .          .          ...          .          .          .       8-51 

Solvent  naphthas     .          .  .         .          .          .17-96         „ 

Phenols  .         .         .  .         .         .         .         .     Trace 

Middle  oils       .  .          .          .          .         .         .     29-14         „ 

Creosote  oils    .         .         .         .  .'  .         .         .     24-26         „ 

Naphthalene    .  .1-28         „ 

Anthracene       .          .          .          .          .          ...       0-93         „ 

Coke       .         ,         .         .         .         .         .         ,.        ,      9-80 

K  K 


498  MODERN   GASWORKS   PRACTICE 

WATER-GAS  ENRICHING  OIL 

In  the  early  days  of  carburetted  water  gas  in  this  country  the  enriching  medium 
'employed  was  almost  solely  a  Russian  Solar  distillate.  At  the  present  day,  how- 
ever, the  centre  of  supply  has  moved  to  America,  from  which  country  the  residual 
petroleum,  having  a  specific  gravity  of  about  0-85,  is  obtained  in  large  quantities. 
The  gas  engineer,  so  long  as  he  can  obtain  his  oil  for  a  reasonable  price,  does  not 
trouble  very  much  about  its  quality,  although  an  inferior  product  will  soon  make 
its  mark  on  the  working  results  of  the  plant. 

It  has  been  more  or  less  conclusively  proved  that  the  laboratory  analysis  of 
gas  oil  is  of  little  avail  in  determining  the  suitability  of  the  oil  for  carburetting 
purposes.  On  this  account  it  is  unusual  to  subject  consignments  of  the  oil  to 
anything  more  than  the  crudest  tests. 

It  is  general  for  the  gasworks'  chemist  to  draw  off  his  sample  carefully  and  to 
note  the  specific  gravity  of  the  oil ;  but  the  result  affords  him  no  indication 
of  the  gasmaking  qualities,  and  is  merely  a  guide  as  to  the  origin,  upon  which  this 
property  to  a  large  extent  depends.  So  far  as  the  origin  of  gas  oil  is  concerned,  it 
has  already  been  pointed  out  that  practically  all  of  that  imported  now  comes  from 
America.  The  other  suitable  types,  Russian  Solar  distillate,  also  Galician — these 
being  high-grade  oils — have  not  been  imported  for  some  years.  Rumanian  oils  are 
of  a  poorer  character  and  rarely  reach  this  country. 

With  regard  to  gasworks'  tests,  the  only  true  indication  of  the  suitability  of 
an  oil  is  a  practical  trial  run  by  an  engineer  who  knows  the  ins  and  outs  of  the  work- 
ing of  his  plants.  Oils  have  frequently  been  known  to  give  satisfactory  laboratory 
tests  in  every  way,  and  yet  to  yield  unsatisfactory  results.  Petroleum,  being  a  natural 
product,  is  liable  to  considerable  variation,  and  no  agents  for  gas  oil  will  guarantee 
results  or  "  candles  per  gallon."  For  American  oils  the  specific  gravity  should  fall 
between  0-845  and  0-865.  The  test  for  flash  point  is  important,  owing  to  the  fact 
that  if  this  falls  below  73°  Fahr.  a  special  licence  for  storing  is  required,  while  higher 
rates  will  be  demanded  for  railway  carriage.  The  test  may  best  be  carried  out  by 
means  of  the  Abel  "  closed  "  apparatus,  and  affords  a  fair  indication  as  to  the  per- 
centage of  volatile  constituents.  The  details  of  the  test  need  not  be  described  here, 
and  it  will  be  sufficient  to  recall  that  the  flash-point  of  an  oil  is  the  temperature 
at  which  it  gives  off  sufficient  vapour  to  ignite  momentarily  on  the  introduction  of 
a  spark  or  flame.  The  oil  is  heated  at  a  prescribed  rate,  and  a  definite  ignition 
agent  is  applied  in  a  given  manner. 

One  of  the  most  satisfactory  methods  of  testing  a  gas  oil  destined  for  water-gas 
manufacture  is  to  ascertain  by  fractional  distillation  whether  or  not  it  is  of  a  homo- 
geneous nature ;  that  is  to  say,  not  merely  a  mechanical  mixture  of  different  oils 
likely  to  separate  out  when  stored  in  a  tank.  A  suitable  homogeneous  oil  would 
give  fractions  coming  away  with  fair  regularity  between  the  second  and  eighth  or 
ninth  10  per  cent,  periods.  The  proportion  of  the  oil  distilling  over  at  a  temperature 
of  less  than  600°  Fahr.  should  also  be  noted  ;  this  should  be  as  low  as  possible,  for 
the  reason  that  a  high  yield  of  these  fractions  indicates  a  tendency  towards  undue 


WATER   GAS  499 

volatility.  More  than  10  per  cent,  remaining  at  750°  Fahr.  would  show  the  presence 
of  undesirably  heavy  constituents  ;  while  the  specific  gravity  of  the  various  fractions 
should  show  a  fairly  uniform  progressive  rise.  Uneven  jumps  at  various  tempera- 
tures are  not  a  recommendation. 

THE  STANDARD  TEST 

The  solid  residue  remaining  after  the  completion  of  fractionation  is  of  no  little 
importance,  and  should  never  exceed  2  per  cent,  by  weight  of  the  original  quantity  of 
oil  taken  ;  in  many  cases  the  figure  will  be  found  to  be  below  1  per  cent.  Mexican 
oil  will  usually  leave  a  far  greater  solid  residue,  occasionally  amounting  to  more 
than  5  per  cent. 

The  standard  test  for  oil  which  is  carried  out  at  many  of  the  larger  gasworks 
is  to  distil  10  fluid  ounces  in  a  special  apparatus,  and  to  carry  the  temperature  up 
to  660°  Fahr.,  this  latter  point  being  gradually  arrived  at  in  a  period  of  40  minutes. 
The  residue  remaining  behind  is  then  cooled,  and  its  specific  gravity  noted.  If 
the  oil  is  of  a  desirable  quality  the  gravity  will  be  0-900.  Probably  one  of  the  most 
important  items  is  the  sulphur  content,  and  this  should  not  be  allowed  to  exceed 
04  to  0-5  per  cent.  The  quantity  of  water  is  also  to  be  watched,  and  may  be  con- 
veniently estimated  by  use  of  a  "  Sutherland  bulb."  The  rougher  test  for  all  oils 
which  lose  an  inappreciable  percentage  of  hydrocarbons  on  being  heated  to  230° 
Fahr.  is  to  weigh  25  grammes  in  a  glass  dish,  heating  to  this  temperature  on  a  sand 
bath,  and  continually  stirring  until  bubbles  of  steam  cease  to  form.  The  sample 
is  then  allowed  to  cool,  and  is  re-weighed,  when  the  loss  of  weight  in  grammes,  multi- 
plied by  four,  represents  the  percentage  of  water  present. 

Although  of  considerable  importance,  owing  to  its  effect  on  the  sulphur  im- 
purities of  the  gas,  the  test  for  sulphur  is  seldom  carried  out  on  gasworks.  A  con- 
venient method  of  obtaining  an  idea  as  to  the  quantity  of  sulphuretted  hydrogen 
is  to  hold  at  intervals  a  piece  of  moistened  lead  acetate  paper  above  the  outlet  of  the 
condenser  ;  if  sulphuretted  hydrogen  is  present  the  paper  will  be  blackened  in  the 
usual  manner,  the  degree  of  blackening  giving  a  fair  indication  of  the  amount  of 
sulphur  in  the  oil.  The  total  sulphur  present  can  conveniently  be  arrived  at  by 
Carius's  method,  or  by  the  use  of  the  bomb  calorimeter ;  but  for  gasworks'  pur- 
'poses  a  ready  means  would  be  that  of  taking  a  weighed  quantity  of  oil,  mixing  it 
with  a  spirit  (such  as  alcohol)  entirely  free  from  sulphur,  and  then  burning  it  in  a 
suitable  lamp.  The  products  are  collected  in  an  apparatus  similar  to  that  prescribed 
by  the  metropolitan  gas  referees  for  testing  sulphur  compounds.  Other  refinements 
of  oil  testing  include  the  use  of  the  calorimeter  and  tintometer.  But  such  apparatus 
is  usually  beyond  the  scope  of  the  average  gasworks. 

THE  THERMAL  EFFICIENCY  OF  A  WATER-GAS  PLANT 

By  means  of  a  series  of  experiments  carried  out  in  America,  A.  Gr.  Glasgow 
has  calculated  the  actual  heat  efficiency  of  a  carburetted  water-gas  plant.  Although 
his  research  was  undertaken  some  twenty-five  years  ago  the  results  have  not  as  yet 
been  challenged  or  supplemented  by  others.  In  this  case  the  water-gas  plant  was 


500 


MODERN   GASWORKS   PRACTICE 


operated*  with  anthracite,  and  not  coke,  and  it  was  first  necessary  to  ascertain  the 
weights,  temperatures,  composition,  etc.,  of  the  raw  materials  and  finished  products. 
With  regard  to  some  of  the  data  obtained  the  following  list  of  temperatures  will 
prove  interesting  to  all  makers  of  water  gas  : — 


Gas  issuing  from  superheater  .          , 

Blast  gases  issuing  from  superheater 

Oil  leaving"  preheater 

Blast  entering  generator 

Steam       „  „  ..-''. 

Ash,  etc.,  withdrawn  from  generator 


1,450C 
1,550C 

235C 
76C 

331 c 
1,560C 


Fahr. 


The  heat  absorbed  by  the  apparatus  is  represented,  on  a  basis  of  1 ,000  cubic  feet 
of  the  carburetted  gas,  first  by  the  amount  of  fuel  fed  into  the  generator.  This 
was  found  to  be  23-5  Ib.  per  1,000  cubic  feet,  after  deducting  unconsumed  anthracite 
found  with  the  ash.  Secondly,  there  is  the  total  heat  entering  with  the  steam ; 
and,  thirdly,  the  sensible  heat  entering  with  the  blast.  The  various  sources  in  which 
this  heat  is  dispersed  are  shown  in  the  following  table  :— 

DISTRIBUTION  OF  ENERGY  PER  1,000  CUBIC  FEET 


B.Th.U. 

Equivalent 
in  Pounds 
of  Carbon. 

A,  heat  of  combustion  of  carbon  

340,750 

oq.e 

B,  total  heat  in  entering  steam      ...                             ... 

18  359 

1.OKR 

C,  sensible  heat  in  entering  blast  ...                             ... 

715 

.(\ACi 

Total  heat  above  60°  Fahr.  fed  into  apparatus  on  fuel  account 

359,824 

24-815 

D,  energy  of  CO  in  water  gas  

90591 

fi-  948 

E,  energy  of  H  in  water  gas    

108  908 

7.K1  I 

F,  sensible  heat  in  escaping  illuminating  gas,  vapours,  etc.    . 
G,  sensible  heat  in  escaping  blast  products  

35,583 

70,838 

2-454 

•i-SS^ 

H,  heat  lost  by  radiation  from  shells  

12454 

tfiJtt 

J,  heat  carried  away  from  shells  by  convection      .... 

15696 

1  -OS^ 

K,  heat  rendered  latent  in  gasification  of  oil     

21  393 

1-47*; 

L,  sensible  heat  in  ash  and  unconsumed  coal  recovered    . 

3,712 

•256 

Total  energy  accounted  for        

359  175 

24-771 

Unaccounted  for  (-18  per  cent.)     .      . 

649 

.04-4 

The  final  profit  and  loss  account  is,  therefore,  as  follows  : — 

B.Th.U.  Lbs. 

Energy  utilized   ...'-..          .          .         .     220,892  15-234 

wasted  .  .  ...         ,     138,283  9-537 

„       unaccounted  for  .  649  0-044 


Total 


359,824 


24-815 


WATER   GAS  501 

Assuming  the  unaccounted-for  energy  to  be  wasted,. this  leaves  a  heat  efficiency 
of  61 '4:  per  cent. 

If  the  oil  fed  into  the  plant  is  taken  into  consideration  as  a  further  source  of 
heat  the  result  will  be  somewhat  modified.  In  Glasgow's  experiments  5  gallons 
of  crude  petroleum  were  admitted  per  1,000  cubic  feet  of  gas.  The  oil  has  a  calorific 
power  of  approximately  18, SCO  B.Th.U.  per  lb.,  and  5  gallons  would  weigh  35  Ib. 
Therefore  :— 

Heat  entering  with  oil  ==  35  X  18,500  =  647,500  B.Th.U.  Adding  this  to  the 
above,  the  total  energy  supplied 

=  359,824  -f-647,5CO  =  1,007,324    B.Th.U.    per    1,000   cubic   feet   of  gas. 

The  calorific  power  of  the  gas  was  found  to  be  720'987  B.Th.U.  per  cubic  foot, 
and  the  quantity  of  tar  recovered  was  5  lb.,  its  calorific  value  being  assumed  the 
same  as  that  of  the  petroleum.  Therefore,  the  heat  recovered  was  : — 

1,000  cubic  i'eet  of  gas  x  720-987  =  .         .         .         .     720,987  B.Th.U. 
5  lb.  of  tar  x  18,500  =  .  .  92,500 


Total         .         .         .     813,487 
On  this  basis,  the  heat  efficiency  arrived  at  is  equivalent  to  80-76  per  cent. 

MODIFICATIONS  OF  WATER-GAS  PLANT 

During  recent  years  there  has  been  some  tendency  towards  the  modification 
of  water-gas  plant,  with  the  result  that  in  some  instances  apparatus  of  a  novel  char- 
acter is  to  be  found  at  work.  One  such  instance  is  the  plant  for  the  production 
of  what  is  technically  known  as  "  Methane-Hydrogen  "  gas,  a  semi-water  gas 
enriched  by  means  of  coal  gas  tar. 

Methane-hydrogen  gas  differs  from  ordinary  water  gas  in  many  respects.  It 
burns  with  a  decided  yellow,  instead  of  a  blue,  flame,  this  being  due  to  the  high 
percentage  of  methane  present,  whilst  the  proportion  of  CO  shows  some  considerable 
reduction  as  compared  with  "  blue  "  gas.  The  approximate  composition  of  methane- 
hydrogen  gas  is  as  follows  : — 

Methane       .........  19  per  cent. 

Carbon  monoxide.          .......  29 

Carbon  dioxide     .          .  .          .          .          .          .3 

Hydrogen     .........  42 

Unsaturated  hydrocarbons     ......  1 

Nitrogen       ..........  5-8 

Oxygen         .         .               •  .         .         .         .         .         .  0-2 

In  the  plant  for  the  manufacture  of  this  type  of  gas  the  depth  of  fuel  in  the 
generator  is  nearly  double  that  in  the  ordinary  carburetted  water-gas  generator, 
but  the  lower  portion  only  is  raised  to  incandescence  by  the  air  blast  admitted 
to  the  base.  About  mid-way  up  the  generator  the  products  of  the  "  blow  "  are 
removed  through  special  ports,  thus  maintaining  the  upper  portion  of  the  fuel 
bed  at  a  moderate  heat.  During  the  "  run  "  tar  is  injected  as  well  as  steam,  the 
former  being  split  up  into  carbon  and  methane.  The  carbon  is  filtered  out  by  the 
cool  upper  portion  of  the  bed,  and  gradually  descends  into  the  zone  of  combustion. 


502 


MODERN   GASWORKS   PRACTICE 


OirrLCT  TO  SUCKS, 

A  ISO  STEMS.  OIL  IN D 
CIRCULATING  C4S  INLET 


THE  "DOUBLE-GAS"  PLANT 

One  of  the  most  interesting  gasmaking  plants  erected  quite  recently  at  a  few 
gasworks  in  this  country  is  one  which  is  designed  to  completely  gasify  both  coal 

and  coke  in  one  operation.  Thusy 
the  coal-gas  plant  and  water-gas 
installation — usually  two  distinct 
pieces  of  apparatus — are  com- 
bined in  one.  The  plant  is  gener- 
ally known  as  Smith's  modifica- 
tion of  the  "  K.  &  A."  patents. 
In  the  original  "  K.  &  A." 
plant  the  system  entails  the  use 
of  two  distinct  generators,  which 
are  "  run "  through  in  series 
and  "  blown  "  through  in  parallel, 
thus  complying  with  the  necessity 
of  arranging  for  a  deep  fuel  bed 
during  the  "  run  "  and  a  shallow 
fuel  bed  during  the  "  blow."  In 
the  latest  type  (Fig.  338)  of  plant 
the  same  procedure  is  arranged 
for,  but  there  is  only  one  generat- 
ing vessel,  instead  of  the  two, 
thus  reducing  capital  outlay  and 
minimizing  heat  losses.  The  out- 
side shell,  being  of  an  oval  cross- 
section,  is  divided  into  two  parts 
by  a  plate  suspended  from  the 
centre  and  reaching  within  a 
short  distance  of  the  base.  The 
spaces  on  either  side  of  this  mid- 
feather  form  the  two  generators, 
whilst  room  is  also  found  for 
special  compartments,  known  as 
"  regenerators."  It  will  be 
noticed  from  the  sectional  sketch 
that  each  generator  is  made  up 
of  two  distinct  portions,  namely, 
the  larger  round  coke  receptacle 
at  the  base,  whilst  the  upper  tapered  portion  is  D-shaped  (not  round)  and  forms, 
among  other  duties,  a  charging  pouch  for  the  coke  or  coal.  It  will  be  seen  that 
at  the  upper  end  of  the  lower  generator  a  series  of  "  nostril "  holes  are  arranged 
for.  The  grouping  of  these,  together  with  the  shape  of  the  upper  generators,  can  be 
best  seen  by  referring  to  the  sectional  view. 


BUST  INLET 

' 


FIG.  338. — SMITH'S  "DOUBLE"  GAS  PLANT. 


WATER   GAS  503 

The  D- shaped  portions  of  the  generators  are  provided  with  an  outlet  at  the 
top,  whilst  the  regenerators  have  ports  which  serve  the  purpose  of  both  inlets  and 
outlets.  A  single  blast  inlet  (the  "  blow,"  by  the  way,  is  a  positive  one)  is  provided 
midway  between  the  two  generators,  between  the  fire-bars.  The  inlet,  therefore, 
does  duty  for  either  generator. 

As  the  plants  so  far  erected  have  been  primarily  put  down  with  the  idea  of 
making  "  blue  "  or  uncarbtiretted  water  gas,  the  method  of  operating  them  for  this 
purpose  will  be  first  described.  Assuming  that  the  generators,  both  upper  and 
lower,  are  charged  up  and  that  the  heats  have  been  got  up,  a  "  blow  "  is  first  of  all 
arranged  for  by  admitting  the  blast  through  the  inlet  shown  in  the  centre  of  the 
plant.  This  current  of  air  then  splits  up  into  two  streams  and  travels  through 
both  coke  beds  simultaneously  as  far  as  the  nostrils.  Owing  to  the  valves  at  the 
top  of  the  D-shaped  generators  being  closed,  the  products  of  the  "  blow  "  cannot 
force  an  exit  this  %ay  ;  hence  they  pass  through  the  "  nostrils,"  traverse  the  regener- 
ators, and  finally  go  out  into  the  air  by  means  of  the  stack  valves.  In  this  way  the 
fuel  in  the  generators  is  brought  up  to  the  desired  temperature,  whilst  the  products, 
in  passing  through  the  "  regenerators,"  give  up  a  further  quantity  of  heat,  so  that 
the  regenerators  are  maintained  at  a  considerable  temperature.  The  gases  leaving  the 
lower  generators  and  passing  through  the  nostrils  contain,  on  an  average,  about 
10  per  cent,  of  carbon  monoxide,  and  this  is  further  burned  to  C02  by  the  admission 
of  secondary  air  at  the  points  shown  in  the  sectional  figure.  The  "  blow  "  in  this 
way  usually  continues  for  rather  more  than  a  minute.  At  the  end  of  this  time, 
the  blast  having  been  shut  off  and  the  stack  valves  closed,  steam  is  admitted  at  the 
top  of  the  regenerator  on  one  side  only.  Passing  downwards  around  the  heated 
chequer  work,  it  is  partly  split  up  and  then  travels  first  through  one  coke  bed  and 
finally  through  the  second.  In  this  way  long  contact  with  the  fuel  and  thorough. 
"  reducing  "  is  assured.  Leaving  the  second  fuel  bed,  the  water  gas  already  pro- 
duced does  not  pass  through  the  nostrils  (the  snift  valve  being  closed),  but  forces 
its  way  through  the  cool  core  of  fuel  in  the  D-shaped  pouch.  It  then  passes  into  the 
special  hydraulic  main  and,  finally,  through  the  scrubber.  One  of  the  chief  advan- 
tages of  passing  the  hot  gas  through  the  incoming  coke  in  this  way  is  that  the  greater 
part  of  the  moisture  is  driven  off  from  the  fuel ;  and,  moreover,  the  outgoing  gas  is. 
thoroughly  filtered. 

In  the  cycle  just  described  no  mention  has  been  made  as  to  how  carburation 
is  effected.  For  this  purpose  air  from  a  compressor  is  admitted  to  the  surface  of 
the  oil  in  a  storage  receiver,  when  the  oil  is  forced  out  at  a  pressure  of  from  30  to  40  IK 
per  square  inch,  through  a  special  regulating  spray  and  into  the  top  of  the  regener- 
ator. Each  regenerator  is  fitted  with  such  a  spray,  but  the  oil  is  only  admitted 
to  that  one  surrounding  the  top  of  the  generator  through  which  the  gas  is  finally 
passing.  The  oil  gas  is  accordingly  forced  downwards  by  its  pressure,  passes 
through  the  nostrils,  and  meets  the  upgoing  stream  of  "  blue  "  water  gas.  The 
two  are  then  thoroughly  intermixed  during  their  passage  through  the  cooler  coke 
core. 

With  regard  to  the  duration   of   "  runs  "   and    "  blows,"   it  is  usual,  after  a> 


504  MODERN   GASWORKS   PRACTICE 

one-minute  "  blow,"  to  admit  steam  for  five  minutes.     After  the  following  "  blow  " 
the  direction  of  the  steam  is  reversed. 

When  the  plant  is  used  for  carbonizing  coal  and  gasifying  the  resultant  coke 
it  is  fitted  with  two  automatic  feed  hoppers  which  are  regulated  to  provide  what 
practically  amounts  to  a  continuous  charge.  During  the  five-minutes'  "  run  "  the 
hot  gas  evolved  from  the  lower  portion  of  the  bed  passes  up  through  the  cooler  zone 
and  partly  carbonizes  the  coal.  The  latter  gradually  works  its  way  down  the 
upper  portion  of  the  generator,  undergoing  more  and  more  complete  carbonization 
during  its  travel.  In  general,  it  is  usually  reduced  to  the  state  of  ordinary  coke 
by  the  time  it  has  passed  two-thirds  the  way  down  the  D-shaped  portions  of  the 
generator.  Thus  during  the  "  run  "  water  gas  is  being  evolved  from  the  coke  and 
coal  gas  from  the  coal,  the  two  intermixing  and  passing  out  at  the  top  of  the  gener- 
ator. In  this  way,  by  the  complete  gasification  of  both  coal  and  coke,  about  60,000 
cubic  feet  of  gas  having  a  calorific  power  of  380  B.Th.U.  per  cubic  foot  may  be 
obtained  from  a  ton  of  coal. 

THE  RINCKER-WOLTER  PLANT 

The  system  known  as  the  Rincker-Wolter  has  been  working  for  some  years 
at  the  Utrecht  gasworks,  and  the  plant  seems  to  have  proved  itself  an  effective  and 
economical  adjunct  to  the  coal-gas  apparatus.  Its  chief  dissimilarity  from  other 
plants  lies  in  the  fact  that  waste  oil,  however  dirty  or  inferior,  may  be  employed 
for  carburetting  purposes.  Both  coal-gas  and  water-gas  tar  have  been  used. 

As  can  be  seen  from  the  diagrammatic  sketch  (Fig.  339),  the  plant  consists 

of  two  identical  generators,  and  no  other  vessels  are  used  for  the  production  and 

•enrichment  of  the  gas.     The  generators  are  lined  throughout  with  fire-bricks,  and 

the  fuel  sprays  pass  through  the  centre  of  the  charging-door  lids.     In  order  to 

"thoroughly  grasp  the  principle  of  the  system,  it  is  essential  that  the  functions  of 

the  various  connexions  on  the  generators  should  be  understood.      Near  the  top  of 

each  generator  is  a  tube  connecting  the  two  shells,  and  by  means  of  this  the  gaa 

produced  in  one  generator  may  pass  to  the  other.     In  addition,  both  generators 

are  fitted  with  primary  and  secondary  air  supplies  from  a  central  blast  pipe.     The 

primary  air  inlets  are  below  the  fire-bars,  whereas  the  secondary  air  is  admitted 

at  a  point  on  a  level  with  the  top  of  the  fuel  bed.     There  is  a  gas  outlet  to  each 

generator.     These  are  below  the  fire-bars,  and  they  split  up  into  a  two-way  pipe, 

one  branch  of  which  leads  to  a  stack-pipe,  the  other  passing  to  a  hydraulic  main 

which  connects  the  generator  to  the  cooling  and  washing  apparatus.     Each  generator 

is  fitted  with  a  steam  supply,  the  steam  being  introduced  beneath  the  fuel  bed,  in 

the  usual  way. 

The  apparatus  is  started  in  the  same  way  as  the  ordinary  water-gas  plant ; 
that  is,  a  wood  fire  is  first  kindled  and  the  coke  bed  is  gradually  built  up  on  this. 
When  the  fires  in  both  generators  are  thoroughly  started,  and  the  coke  is  on  a  level 
with  the  secondary  air  inlets,  the  air-blast  is  admitted  below  the  fuel  in  (say)  the 
right-hand  generator  and  above  the  fuel  in  the  left-hand  generator.  For  the  sake 


WATER   GAS 


505 


of  simplicity  in  describing  the  operations,  it  will  be  of  advantage  to  designate  the 
right-hand  generator  as  No.  1,  the  left-hand  being  No.  2. 

Before  blowing  is  commenced,  the  stack- valve  on  No.  1  generator  is,  of  course, 
shut,  whereas  that  on  No.  2  generator  is  opened.  In  this  way,  the  direct  air-blast 
raises  to  a  certain  extent  the  temperature  of  the  fuel  bed  in  No.  1  generator,  but, 
as  combustion  is  incomplete,  a  stream  of  producer  gas  is  passing  through  the  top 
connecting  tube  into  the  second  generator.  This  combustible  gas  then  comes  into 
contact  with  the  secondary  air-blast,  and  its  consequent  combustion  provides 
sufficient  heat  for  raising  the  temperature  of  the  fuel  in  this  generator.  The  hot 
gases  pass  downwards  through  the  coke  bed,  and  then  away  through  the  open  stack 
valve. 


FIG.  339. — THE  "  RINCKER-WOLTER  "  WATER-GAS  PLANT. 

It  is  advisable  to  secure,  as  far  as  possible,  nearly  equal  temperatures  in  both 
vessels,  and  in  order  to  do  this  the  sequence  of  generators  is  reversed  after  a  period 
of  about  two  minutes.  Thus  the  primary  blast  is  admitted  to  No.  2  generator, 
and  the  producer  gas  meets  with  the  secondary  air  in  the  top  of  No.  1. 

By  heating  the  generators  in  this  way  for  some  time  a  temperature  sufficiently 
high  for  gasmaking  is  obtained. 

CYCLE  OF  OPERATIONS 

In  the  Rincker-Wolter  plant  the  gasmaking  "  run  "  usually  lasts  for  about  six 
minutes,  but  it  is  unique  in  that  no  steam  is  admitted  to  the  generators  during  the 
first  half  of  the  period.  Before  the  "  run  "  is  commenced,  the  various  air  valves 
and  flue  dampers  are  necessarily  closed  and  a  passage  is  made  for  the  gas  by  opening 
the  valve  at  the  outlet  of  the  hydraulic  main  or  "dipper."  The  generators  are, 
of  course,  always  operated  in  series  for  "  blowing,"  whilst  gasmaking  is  carried  on 
in  each  one  alternately.  Assuming  that  a  "  run  "  has  just  commenced  in  No.  1 
generator,  then  the  oil,  or  other  carburetting  agent  employed,  after  passing  through 
a  meter,  is  sprayed  on  to  the  coke  in  this  generator. 


506 

On  coming  into  contact  with  the  incandescent  coke,  the  oil  is  immediately 
gasified,  and  passes  off  through  the  bottom  of  the  generator  to  the  hydraulic  main, 
where  the  tarry  matter  and  particles  of  carbon  are  retained.  At  the  expiration  of 
about  three  minutes,  the  oil  is  shut  off  and  steam  is  blown  through  the  same  spray 
—partly  for  cleaning  purposes — for  a  period  of  about  seventy-five  seconds.  The 
No.  1  "  dipper  "  valve  is  then  closed,  the  corresponding  valve  on  No.  2  being  opened. 
Steam  is  then  injected  under  the  fire-bars  of  No.  1  generator  for  one  minute,  and  the 
gas  produced  passes  through  the  connecting  pipe  and  second  fuel  bed  to  the  opposite 
hydraulic  main.  The  steam  is  now  shut  off,  and  gives  way  to  a  blast  of  air,  which 
is 'continued  for  a  few  seconds,  and  thoroughly  scours  the  apparatus. 

From  the  above  description,  it  may  appear  that  a  somewhat  complicated  series 
of  operations  are  comprised  in  the  "  run."  The  cycle  is,  of  course,  more  or  less 
intricate  when  compared  with  the  water-gas  systems  in  common  use  in  this  country. 
It  will  easily  be  grasped,  however,  by  tabulating  the  working  as  follows  : — 

Oil  sprayed  in  (say)  No.  1  generator.          .....       3  minutes. 

Steam  blown  through  spray        .         ,         ...          .          .75  seconds. 

No.  1  "  dipper  "  valve  closed  and  No.  2  "  dipper  "  opened. 

Steam  admitted  under  fire-bars  of  No.  1.   .          .         .          .         .       1  minute. 

Air  admitted  to  No.  1  .  .          .          .'        .    about  10  seconds. 

Total  period  of  "  run"  about  6  minutes. 

After  the  completion  of  the  above  "  run,"  the  blowing  cycle,  as  previously 
described,  commences,  and  continues  for  about  two  minutes.  The  "  run " 
is  then  resumed,  but  with  the  difference  that  the  first  generator  in  the  preceding 
cycle  now  becomes  second  in  the  sequence.  This  alternate  operation  of  the 
generators  causes  practically  similar  working  conditions  for  both  vessels  as 
regards  temperature  and  consumption  of  coke  and  oil. 

THE  INDUSTRIAL  USES  OF  WATER  GAS 

In  addition  to  being  used  as  an  auxiliary  to  coal  gas,  blue  water  gas  has  within 
recent  years  been  applied,  with  very  satisfactory  results,  to  the  welding  of  plates 
and  heating  of  furnaces  and  forges.  This  method  has  proved,  of  great  practical 
advantage  in  welding  tubes  for  gas,  water  and  steam  mains,  for  boiler  work  and 
also  for  melting  steel.  Tests  conducted  by  the  Admiralty  show  the  strength  of  a 
"  blue  "  gas  weld  to  be  equal  to  that  of  the  plate.  Having  a  very  much  higher 
calorific  power  than  producer  or  suction  gas,  "  blue "  water  gas  may  be 
used  for  driving  gas-engines,  the  consumption  being  al)out  35  cubic  feet  per  B.H.P. 
hour.  The  consumption  of  ordinary  suction  gas  is  about  80  cubic  feet  per  B.H.P. 
hour.  No  water  gas,  however,  is  entirely  satisfactory  when  used  for  power,  for  the 
large  proportion  of  hydrogen  prevents  high  compression  in  the  cylinder  of  the 
engine. 

By  far  the  most  important  property  of  "  blue  "  gas  is  its  exceedingly  high  flame 
temperature.  Dr.  Roessler  has  found  that  by  admixture  with  heated  air  a 
temperature  considerably  above  the  melting  point  of  platinum  may  be  easily  ob- 
tained. Under  general  conditions,  however,  the  temperature  of  the  hottest  part 


WATER    GAS  507 

of  the  flame  is  about  2,800°  to  3,000°  Fahr.  It  is  owing  to  this  property  that  "blue" 
gas  is  applicable  to  such  processes  as  welding  and  forging,  and  for  use  in  furnaces. 

In  all  processes  of  the  above  kind,  there  is  no  necessity  to  purify  the  gas  from 
sulphuretted  hydrogen — merely  an  ordinary  water-scrubber  is  used.  It  is,  in  fact,, 
an  advantage  to  leave  the  gas  unpurified,  for  it  then  has  a  distinct  smell,  and  any 
escape  may  be  quickly  perceived.  Thus  one  of  the  greatest  drawbacks  to  "blue" 
gas — its  freedom  from  smell — is  more  or  less  overcome.  In  Germany  it  has  in 
some  cases  been  thought  advisable  to  impart  a  distinct  odour  to  the  gas,  by  pass- 
ing it  through  a  heavy  hydrocarbon  oil,  such  as  mercaptan. 

A  new  process  for  which  water  gas  may  be  employed,  and  one  which  will  probably 
be  largely  developed  in  the  future,  is  that  of  producing  hydrogen.  This  is  done  by 
liquefying  or  freezing  out  all  the  other  constituents — the  hydrogen,  which,  of  course, 
liquefies  at  a  much  lower  temperature,  being  left  behind. 

Cement  manufacturers  are  now  making  use  of  water  gas,  which  is  introduced 
into  the  revolving  kiln  for  the  finishing- off  process,  and  it  is  also  finding  its  way  into 
the  brick-making  industry. 

STEAM  GENERATION  ON  GASWORKS 

The  large  and  ever-increasing  extent  to  which  carburetted  water  gas  manufacture 
has  been  adopted  in  modern  gasworks  has  placed  gas  authorities  amongst  the 
chief  users  of  steam  for  manufacturing  purposes.  The  importance  of  this  section 
of  the  works'  equipment  warrants  a  more  detailed  study  than  it  is  possible  to  include 
in  the  present  work,  and  it  is  proposed  only  t*  consider  broadly  the  more  important 
factors  which  usually  govern  the  selection,  lay-out,  and  operation  of  steam  generat- 
ing plant. 

SELECTION 

The  principal  factors  which  usually  determine  the  type  of  boiler  selected  are 
unit  evaporative  capacity  for  a  given  floor  space,  where  this  is  an  important  con- 
sideration ;  but  in  a  lay-out  for  a  new  works  more  importance  would  be  attached 
to  convenience  of  handling  fuel  and  ash,  arrangement  of  main  flues,  and  provision 
for  spare  plant  and  extensions.  Steam  generating  plant  is  usually  designed  and 
rated  on  the  assumption  that  some  kind  of  natural  coal  fuel  will  be  the  staple  fuel 
used,  and  the  influence  of  coke  or  breeze  (which  may  be  taken  as  the  staple  solid 
steam  raising  fuel  of  the  gasworks)  on  the  steaming  capacity  of  the  boilers  ha& 
to  be  borne  in  mind  in  making  a  selection. 

TYPES   OF   GENERATORS 

Broadly,  there  are  in  present  use  two  types  of  boilers,  each  having  their  special 
features,  namely,  the  water-tube  or  externally  fired  boiler,  typified  in  the  Babcock 
and  Wilcox  pattern,  and  the  fire-tube  or  internally  fired  Cornish  and  Lancashire 
types.  When  capacity  and  limited  floor  space  are  the  chief  factors,  the  range  of 
selection  is  limited  to  the  various  patterns  of  the  former  type,  which  have  usually 
a  ratio  of  heating  surface  to  grate  area  of  50  or  60  to  1,  as  compared  with  about  25 


508  MODERN   GASWORKS   PRACTICE 

to  1  available  in  the  Lancashire  type.  For  rapid  steaming  and  quick  response  to 
,sudden  heavy  demands,  the  water-tube  boiler  is  now  recognized  as  the  more  sensi- 
tive, but  'the  greater  steam  and  water  reserve  capacity  of  the  Lancashire  type  boiler 
renders  it  the  more  suitable  for  the  intermittent  heavy  pulls  of  the  water  gas  plant. 
To  realize  the  advantages  of  both  types  a  combination  battery  working  in  parallel 
Jias  been  found  to  be  most  effective  in  responding  to  the  severest  conditions  imposed. 
In  the  matter  of  thermal  efficiency  there  would  appear  to  be  little,  if  any,  in  favour 
of  either  type. 

GRATE   AREA 

The  economic  rate  of  combustion  of  fuel  and  the  area  of  the  boiler  fire-grates 
determine  the  normal  evaporative  capacity.  With  coke  as  fuel,  22  Ibs.  to  25  Ibs. 
per  sq.  ft.  of  grate  area  per  hour  represent  the  economic  average  maxima  for  hand- 
fired  fixed  grates.  Higher  rates  may,  of  course,  be  attained,  but  only  at  the  expense 
of  efficiency.  Probably  18  Ib.  to  20  Ib.  would  represent  the  best  normal  working 
rate  for  average  coke  or  breeze.  The  limiting  factor  in  grate  area  in  the  Lancashire 
type  boiler  is  the  length  of  grate  which  a  man  may  efficiently  stoke  and  clinker, 
usually  6  ft.  6  ins.  to  7  ft.  6  ins.,  measured  from  the  furnace  front.  This  factor  limits 
the  total  effective  area  to  36  or  38  sq.  ft.  in  the  larger  capacity  boilers  of  this  type. 
Now,  assuming  evaporative  values  for  coke  and  breeze  respectively  of  9  Ib.  and 
5  Ib.  of  steam  per  Ib.  of  fuel,  as  fired,  the  steaming  capacity  at  the  various  rates  of 
filing  indicated  may  be  accurately  arrived  at.  To  the  gas  engineer,  the  relatively 
large  proportion  of  grate  area  obtainable  in  the  water-tube  boiler  is  certainly  an 
attractive  feature,  having  in  mind  the  characteristics  of  the  staple  fuel. 

'     DRAUGHT        „    . 

Except  perhaps  where  an  existing  chimney  shaft  provides  the  necessary  draught, 
some  system  of  impelled  draught  may  be  "  induced  "  or  "  forced,"  i.e.,  by  means 
of  an  exhaust  fan  located  near  and  discharging  into  the  chimney  shaft ;  or  a  pressure 
fan  applied  to  the  under- side  of  the  fire-grate.  The  induced  system  depends  upon 
the  maintenance  of  a  partial  vacuum  over  the  fire,  but  possesses  the  disadvantage 
of  increasing  the  cold  air  infiltration  through  the  brickwork  setting,  etc.,  while  it 
tends,  by  increasing  the  speed  of  the  waste  gases,  to  carry  over  and  discharge  at 
the  chimney  a  portion  of  the  grit  and  dust,  which,  with  the  "  forced  "  system  properly 
applied,  remains  on  the  grate  or  falls  immediately  beyond  the  bridge  wall  or  first 
baffle.  The  various  types  of  steam-jet  forced  draught  furnaces,  with  one  or  more 
short  chimney  shafts  of  large  area,  are  among  the  most  favoured  systems  now  adopted. 
The  height  to  which  the  boiler  shaft  is  carried,  and  consequently  the  cost  of  con- 
struction, will  be  largely  determined  by  the  system  of  draught  adopted,  whether 
"  natural,"  "  induced,"  or  "  forced.''  The  apparently  beneficial  effect  of  a  limited 
supply  of  steam  on  the  combustion  of  coke  warrants  due  consideration  of  the  steam- 
jet  impelled  system,  applied  either  on  the  closed  ash  pit  or  hollow  fire-bar  principle. 

Various  types  of  steam- jet  forced  draught  furnaces,  permitting  a  comparatively 
.short  chimney  shaft  to  be  used,  have  been  employed  in  conjunction  with  coke  and 


WATER   GAS 


509 


breeze  burning  for  some  years,  but  in  many  cases  the  alterations  have  been  cumber- 
some and  expensive.  The  latest  blower,  introduced  by  the  London  Coke  Committee, 
may  best  be  described  as  providing  an  "  impelled  "  draught,  which  is  admitted 
beneath  the  fire  bars  by  either  two  or  three  delivery  pipes  fashioned  somewhat  on 
the  lines  of  a  Venturi  tube.  The  whole  can  be  fitted  to  a  coal-burning  boiler  in  a 


FIG.  340. — LONDON  COKE  COMMITTEE'S  APPARATUS  FOR  "IMPELLED"  DRAUGHT. 

few  hours,  and  requires  for  its  operation  only  two  to  three  per  cent,  of  the  steam 
raised. 

MECHANICAL   STOKING 

In  the  larger  works  the  possibility  of  automatically  stoking  and  cleaning  boiler 
furnaces  has  led  to  the  adoption  of  mechanical  stokers  of  the  travelling- grate  or 
"  sprinkler  "  type.  The  latter  are  applicable  to  either  water-tube  or  Lancashire 
boilers,  but  so  far  the  application  of  the  travelling-grate  of  the  "  underfeed  "  or 
Babcock  type  has  been  limited  to  water-tube  boilers  of  fairly  high  capacity.  These 
generally  operate  in  conjunction  with  some  system  of  forced  draught.  Rates  of 
30  lb.  of  fuel  per  square  foot  per  hour  are  said  to  be  maintained,  so  that  the  full 
normal  capacity  of  the  boiler  with  this  equipment  may  be  realized  with  coke  fuel. 

SUPERHEAT 

All  steam  engines  are  essentially  heat  engines,  and  the  manufacture  of  water- 
gas  is  essentially  a  heat  process.  Accordingly,  the  use  of  steam  superheaters,  either  as 
an  integral  part  of  the  boiler  unit  or  separately  fired,  is  the  trend  of  modern  practice. 


510  MODERN   GASWORKS   PRACTICE 

ECONOMIZERS 

The  development  of  the  economizer  has  followed  the  recognition  of  the  inef- 
ficiency of  coal  as  a  boiler  fuel,  with  which  fuel  as  much  as  20  per  cent,  saving  may 
be  effected  by  installing  a  suitably  proportioned  economizer  between  a  coal-fired 
boiler  and  its  chimney  shaft.  The  same  would  not,  of  course,  apply  in  the  case 
of  coke-fired  boilers,  in  which  the  heat  of  combustion  appears  to  be  largely  trans- 
mitted to  the  water  and  steam  inside  by  radiation,  and  consequently  there  is  a 
smaller  proportion  of  heat  carried  off  in  the  waste  gases.  Moreover,  as  the  pro- 
portion  of  excess  air  necessary  for  the  complete  combustion  of  coke  is  so  much  less 
than  that  required  with  coal,  a  relatively  smaller  volume  of  gas  comes  in  contact 
with  the  economizer  tubes.  Reliable  tests  show  that  where  an  average  increase  of 
108°  Fahr.  in  feed  temperature  was  obtained  with  a  coal-fired  boiler  fitted  with  an 
economizer  of  the  ordinary  type,  an  average  increase  of  only  78°  Fahr.  was  main- 
tained when  the  same  boiler  was  working  with  coke  fuel  on  a  forced  draught  grate. 
For  each  10°  Fahr.  increase  in  feed  temperature,  a  saving  in  fuel  of  about  one  per 
cent,  is  effected,  so  that  it  would  appear  to  be  somewhat  problematical  whether  the 
initial  cost  and  maintenance  of  economizers  would  be  justified  when  coke  or  breeze 
is  used  as  the  fuel. 


WATER   GAS 


511 


APPROXIMATE  FUEL  COST  OF  EVAPORATION  FROM  AND  AT  212°  FAHR. 
(Compiled  by  E.  W.  L.  Nicol) 


COAL  SLACK. 

HABD  STEAM  COAL. 

SMOKELESS  WELSH  COAL. 

GAS  COKE. 

Mechanically  stoked. 

Hand  fired  : 
Natural  Draught. 

Hand  fired  : 
Natural  Draught. 

Hand  fired  : 
Forced  Draught. 

Atjper  ton. 

Evaporative 
value. 
7-5  Ib. 

At  per  ton. 

Evaporative 
value. 
9-5  Ib. 

At  per  ton. 

Evaporative 
value. 
10-5  Ib. 

At  per  ton. 

Evaporative 
value. 
9  Ib.  net. 

t.'d. 
7    0 

per  1,000 
gallons 
evaporated. 
s.  d. 

4    2 

s.  d. 
14    0 

per  1,000 
gallons 
evaporated. 
s.  d. 
6    6 

s.  d. 
16    0 

per  1,000 
gallons 
evaporated. 
s.  d. 
6  11 

s.  d. 
13    0 

per  1,000 
gallons 
evaporated. 
s.  d. 
6    5 

8    0 

4    8 

15    0 

7    0 

17    0 

7    4 

14    0 

6  11 

9    0 

5     4 

16    0 

7     6 

18    0 

7     9 

15    0 

7    5 

10    0 

5  11 

17     0 

7  11 

19    0 

8     1 

16    0 

7  11 

11     0 

6     6 

18     0 

8     5 

20    0 

8     6 

17    0 

8     5 

12    0 

7     1 

19     0 

8  11 

21     0 

8  11 

18    0 

8  11 

13    0 

7     8 

20    0 

9     4 

22    0 

9     4     • 

19    0 

9     5 

14    0 

8    4 

21     0 

9  10 

23    0 

9     9 

20    0 

9  11 

15    0 

8  11 

22    0 

10     4 

24    0 

10     2 

21     0 

10    5 

16    0 

9     6 

23    0 

10     9 

25     0 

10     7 

22    0 

10  11 

17     0 

10     1 

24    0 

11     2 

26    0 

11     0 

23    0 

11     5 

18    0 

10     8 

25    0 

11     8 

27    0 

11     5 

24    0 

11  11 

19    0 

11     4 

26    0 

12     2 

28     0 

11  10 

25    0 

12     4 

20    0 

11  11 

27    0 

12    8 

29    0 

12     4 

26    0 

12  10 

21     0 

12     6 

28    0 

13     1 

30    0 

12     9 

27    0 

13     5 

22    0 

13     1 

29    0 

13     7 

31     0 

13     2 

28    0 

13  11 

23    0 

13     8 

30    0 

14    0 

32    0 

13     7 

29    0 

14     5 

24    0 

14     4 

31     0 

14     6 

33    0 

14     0 

30    0 

14  10 

25    0 

14  11 

32    0 

15     0 

34    0 

14     5 

31     0 

15     4 

26    0           15     6           33    0 

15     6 

35    0 

14  10 

32    0 

15  10 

27    0 

16     1 

34    0 

16    0 

36    0 

15     4 

33    0 

16     4 

28    0           16    8 

35    0 

16    5 

37    0 

15     9 

34    0 

16  10 

29    0           17    4 

36    0 

16  11 

38    0 

16     1 

35    0 

17     4 

—                 — 

— 

— 

39    0 

16     6 

— 

~~" 

N.B. — The  average  evaporation  of  a  Lancashire  boiler  is  about  500  gallons  per  hour. 


INDEX 


Acetylene,  degradation  of,  268,  271 

hydrocarbons,  264 

in  coal  gas,  267,  268 

in  gas  liquor,  329 

polymerization  of,  269 
Acts  governing  public  supply  of  gas,  4,  6 
Air,  admission  to  purifiers,  15,  391 

amount  required  for  water  gas  "  blow  ", 
489 

backward  rotation  and,  392 

effect  as  a  diluent,  393 

of  adding  an  excess  of,  393 

of  in  purifiers,  393 

on  wet  purification  plant,  392 

injector  for  purifiers,  392 

meters  for  water  gas  plant,  489 

primary,  66,  92,  97,  98 

regulation  when  starting  up,  84 

rise  of  temperature   in   purifiers  due  to, 
393 

safety  seal  for,  392 

secondary,  50,  66,  72,  73,  84,  92,  98,  99, 
140 

slide,  Brooke's,  85 

sucking  in  of,  92,  168 

supply  to  producers,  42,  49,  52,  55,  66, 

71,  72,  84,  92,  98,  99 
Aliphatic  compounds,  264 
Alkalinated  cellulose,  413,  418 
Alrich  on  gasholder  tanks,  455 
Alternating  current,  227 
Alumina,  in  fireclays,  130 

in  oxide  of  iron,  385 
Aluminous  fireclays,  133 
Amine  bodies  in  gas  liquor,  329 
Amino  compounds,  purification  with,  413,  417 
Ammonia,  absorbed  in  polysulphide  process, 
372 

amount  absorbed  by  water,  326 

artificial  increase  of,  260,  261 

Burkheiser  process  for  recovering,  360 

Cobb  and  Rollings'  research  on,  259 

degradation  of,  266 

direct  method  of  recovering,  358 

effect  of,  in  purification,  369 

expulsion  from  coal,  258 


Ammonia,  Feld  process  for  recovery  of,  362 

formation  of,  258 

free  and  fixed,  328 

heavy  charges  and,  281 

in  coal  gas,  326,  327,  330,  331,  383,  384 

influence  of  temperature  on,  258,  266 

in  gas  liquor,  328,  330 

in  water  gas,  495 

Kopper's  process  for  recovering,  364 

loss  of,  175 

loss  through  scrubbers.  357 

reaction  with  SH2  and  C02,  327 

recovery  in  Mond  plant,  80 

synthetic  formation  of  in  retort,  258 

Tervet's  theory,  259 
Ammonium  acetate  in  gas  liquor,  329 

carbonate,  327,  330,  332 

chloride  in  gas  liquor,  329,  330,  332 

cyanide  in  gas  liquor,  329,  332,  368 

ferrocyanide  in  gas  liquor,  328,  332,  368 

polysulphide  in  gas  liquor,  329,  332 

sulphate  in  gas  liquor,  329,  330,  332 

sulphite  in  gas  liquor,  329,  330,  332 

sulphocyanide  in  gas  liquor,  328,  330, 332, 
368 

thiosulphate  in  gas  liquor,  329,  330,  332 
Analysis  of  blue  water  gas,  496 

coal  gas,  496 

coals,  238,  239 

carburetted  water  gas,  496 

fireclays,  133 

Kerpely  gas,   81 

Mond  gas,  496 

Suction    gas,    496 
Aniline  as  a  coal  solvent,  233 
Annular  condenser,  286,   289 
Anthracene  oil  for  removing  naphthalene,  301 
Anthracite,  233,  234,  235,  236,  238,  240 
Anti-dips,  168 

advantages  of,  168 

Corts',  169 

Davidson's,  168 

Help's,  169 

Simmonds',  169 

Apparent  porosity,  135,  138,  141 
Aqueous  vapour  in  gas,  292,  296 


513 


LL 


514 


INDEX 


Arches,  barrel-shaped,  61 

cost  of,  74 

prevention  of  sagging,  62 

radius  of,  61 

retort  setting,  54,  58 

spandrils  of,  60,  62 
Aromatic   hydrocarbons,   264,  267,  297 
Arrol-Foulis  stoking  machinery,  184,  185 

cost  of,  186 
Ascension  pipes,  159 

admission  of  water  to,  160 

augering,  159 

Bournemouth  type,  162 

cost  of,  74 

pipes,  Darwen  type,  162 

jacketing  for,  161 

jointing  for,  159 

loss  of  heat  in,  94 

precautions  with,  159 

single,  161 

size  of,  159,  161 

stopped,  160,  161 
Ash,  in  coal,  98,  238,  239,  262 

in  coke,  263 

in  producers,  98 

"  Athion  "  purification  process,  413,  418 
Audouin  and  Berard  on  purification,  393 
Auger,  boring,  30 
Augering  pipes,  159,   160 


Back-pressure  in  hydraulic  main,  167 

on  exhausters,  306 
Backward   rotation,   390,   392 
Balance  of  heat  in  retort  setting,  93 

in  water-gas  plant,  499 
Band  conveyors,  207 
Barker's  mill,  352 
Barnum  on  heat  balances,  94 
Barrel-shaped  setting  arch,  61 
Battery  condenser,  288 
Baum  coal  washer,  244 
Beckton  system  of  lime  purification,  398 

water  gas  plant,  475 
Bell,  Ferguson,  on  heavy  charges,  259,  281 

on  naphthalene,  303 
Bell,  stresses  in  gasholder,  440 
Benzene,  amount  in  coal  gas,  269,  302 

degradation  of,  274 

polymerization  from  acetylene,  269 
to  naphthalene,  280 

series  of  hydrocarbons,  264 

structural  formula  of,  265,  266 
Bergius  on  coals,  234 
Berthelot  on  hydrocarbons,  268 
Bill,  necessary  procedure  to  obtain,  4 
promotion  of  a  Gas,  5       *  . 

purchase  clause  in,  5 
Bituminous  coals,  233 


"  Blue  "    water   gas,  '470 

composition  of,  496 
"  Blue"  water  gas,  cost  of,  494 

"  Double-gas  "  plant,  502 

"  K  and  A  "  plant,    478 
Board  of  Trade,  application  to,  5 
Bog  ore,  384 

analysis  of,  385 
Boilers,  blower  for,  509 

cost  of,  24,  25 

draught  required  for,  508 

grate  area  required  for,  508 

position  of,  18 

steam,  on  gasworks,  507 
Bond,  on  temperatures,  282 
Bone,  Professor,  on  hydrocarbons,  265,  270 
Bonny  bridge  fireclay,  134 
Boring,  auger,  30 

trial,  30 

Borings,  for  joints,  157,  159 
Botley's  naphthalene  spray,  303 
Bournemouth  ascension  pipe,  162 
Boyle,  1 
Bracing,  for  chimneys,  65,  74 

for  mouthpieces,  158 

for  retort  settings,  156 
Bremond  on  naphthalene,  303 
Bricks,  stock,  153 

fireclay  (see  under  Refractory  Materials) 
Bridge  pipes,  159,  161 
Bright™   Oil  spray,  493 
British  Cyanides  Co.'s  cyanide  process,  370 
Brooke's  automatic   air   regulator,  85 

regenerator,  70 

rule  for  chimney  area,  64 
Browne,  A.  F.,  on  condensation,  292 
"  Brownox  "  purifying  material,  386 
Brown's  regenerator,  70 
Brunswick  tar-washing  system,  299 
Brunton's  retort,  100 
Buckstays,  cost  of,  74 
Bueb's  cyanide  process,  376 

vertical  retorts,  108,  128 
Buildings,  cost  of  various,  24,  36,  38,  128 

for  purifiers,  25 

for  water  gas  plant,  25 

foundations  for,  32 

modern  types,  35,  41 

steel-framed,  37 
Burgess  and  Wheeler,  270 
Burkheiser  process,  360 
Butterfield,  on  condensation,  296 

on  naphthalene,  302 
Buttress  walls,  58 

Calcium  sulphocyanide,  372 

Calorific  intensity,  49 

Calorific   power,   effect  of  air  on,  393 


INDEX 


Calorific  power,  effect  of  steaming  on,  285 

of  benzene,  267 

of   "blue"   gas,   496 

of  carbon  monoxide,  267 

of  carburetted  water  gas,  496 

of   coal,   96,   236,   243 

of  coal  gas,  496 

of  coke-oven  gas,  120 

of  ethane,  267 

of  ethylene,  267 

of  hydrogen,  267 

of  methane,  267 

of  Mond  gas,  496 

of  producer  gas,  81 

recovered  from  coal,  243 
'Candle  power,  effect  of  air  on,  393 
of  steaming  on,  285 
of  tar  washing  on,  297,  299 

of  benzene,  267 

of  coal  gas,  274,  496 

of  ethane.  267 

of  ethylene,  267 

of  methane,  267,  268 
'Cannel  coal,  239,  244 

Capacity  of  various  units,  12,  19,  72,128,425 
Capital' expenditure,  10,    19,  27,  28,  128,  494 

decreasing,  10 

on  horizontal  retorts,  102,  128 

on  inclined  retorts,  77 

on    stoking    machinery,     75,     185,    188, 
192,  195 

on  vertical  retorts,  102,  128 
Carbon,  calorific  power  of,  267 

dioxide,  effect  on  quality  of  gas,  394 

dioxide  in  coal  gas,  238,  254,    275,   327, 
331,  383,  384 

in  gas  liquor,  330 

distribution  of  in  coal,  255,  262 

disulphide  (see  under  Sulphur  Compounds) 

free,   270,  277,  280 

in  coal,  234,  235,  254,  262,  263 

in  coke,  263 

monoxide  in  gas,  238,  254,  275 
in   water  gas,   468,   470,  486,  496 

oxysulphide,  379,  380 

residuum  in  coal,  235,  236 

volatile,  in  coal,  235 
Carbonization,  253 

continuous,  100 

degradation  during,  266,  268,  275,  279 

heat  balance  of,  95 

heavy  charges  and,  89,  90,  275,  279,  281 

hydrocarbons  and,  263 

nitrogen  and,  256 

primary  products  of,  254 

products   of,   254 

synthetic   reactions   during,  260,  261 

temperature  of,  254,  255,  274,  281 
throughout  charge,  281 


Carbonization,  theory  of,  266,  279 

thermal  nature  of,  243,  280 
Carbonizing  plant,  cost  of,  12,  102,  128 
Carburation  of  water  gas,  491 
Carburetted  water  gas  (see  under  Water  Gas), 

466 

Carpenter's   condenser,  293,  299 
Carpenter-Evans  process,  413 
Catch  boxes,  15,  386,  390,  391 
Cellulose,  234 

.Centrifugal  washer -scrubbers,  343 
Chambers-Ovens,  Koppers',   120,  128 

Munich,  124,  128 

Norwich,  126 

Chamotte  in  fire   bricks,   132 
Charging  machinery  for  retorts,  183 
Chimney,  area  for  settings,  64 

bracing  for,  65,  74 

cost  of,  74 

draught,  66,  68,  84,  86,  97 

design  of,   65 

height  of,   64 

loss  of  heat  in,  94 
China  clay,  130,  132 
Chloroform  as  a  coal  solvent,  233 
Ciselet  and  Deguide's  cyanide  process,  376 
Glaus  liquor  process,  357 
Clay,  allowable  pressure  on,  34 

fire — (see  under  Refractory  materials),  130 
Clayton,  Rev.  John,  1 
Clean  water  scrubber,  333 
Cliff's  composite  retort,  147 
Clinker,  curtailment  of,  51,  97,  98,  126 

slagging  action  of,  140,  153 
Clinkering,   average   period  of,    107,   111, 
126 

machines,  202 

mechanical,  81,  491 

water  gas  plant  and,  490 
Coal,  ammonia  yield  from,  257 

amount  required,  13 

analyses  of  typical  gas-making,  238,  239, 
240,  241,  263 

anthracite,  233,  234,  235,  236,  238,  240, 
244 

ash  in,  98,  238,  239,  262 

artificial  formation   of,   234 

average  transport  rates  for,  241 

bituminous,  233,  235,  237 

"  brasses  "  in,  244 

burning  heap  of,  247 

calorific   power   of   various,  96,  236,  238 

calorific  power  recovered,  243 

cannel,  239,  244 

carbon  in,  234,  235,  238,  239,  254,  262 

carbon  residuum  in,  235,  236 

carbonization  of,  253 

carbonization  of  wet,  248 

charges  in  retort,  89,90, 125,  128,  279,  281 


516 


INDEX 


Coal,  coking  properties  of,  236 

conglomerate,  236 

constitution  of,  235 

contracts  for,  241 

cost  of  washing,  244 

deterioration  of,  244,  249 

endothermicity  of,  243 

examination  of,  233 

formation  of,  234 

gasmaking,  233,  238 

gas  multiple  for,  242 

heavy  charges  of,  89,  90,  275,  279 

hydrocarbons  in,  235,  236,  254 

hydrogen  in,  234,  238,  239,  262 

humus  bodies  in,  235,  236,  254 

impurities  in,  243,  262 

Ibs.  of  sperm  per  ton,  241 

lignite,  233,  234,  235,  237 

methods  of  testing,  241 

moisture  in  washed,  244 

names  of  well-known,  239 

nitrogen  in,  234,  238,  239,  256,  262 

occluded  oxygen  in,  246, 251 

origin  of,  234 

oxygen   in,   234,   237,   238,  239,  262 

price  of,  240 

proximate  analysis  of,  241 

purchase  of,  240 

pyrites  in,  243,  244 

quantity  used  in  U.K.,  238 

resin  bodies  in,  135,  236,  246,  254 

solvents  for,  233 

space  occupied  by,  13,  20,  240 

specific  gravity  of,  234,  240,  243 

spontaneous  combustion  of,    244 

stamping  charge,  120 

steam,  233,  234,  235,  238,  244 

steaming   charge  in  retort,  110,  128 

-stop  for  projectors,  191 

storage  of,  13,  20,  244,  250 

stores,  design  of,  39 

-storing  under  water,  250 

sulphate  of  ammonia  yield  of,  257,  258 

sulphur  in,  238,  239,  261,  262 

temperature   throughout   charge,  281 

"  true  ",  233 

-tunnel  in  store,  250 

unoxidized  hydrogen  in,  237,  256 

virgin  liquor  from,  262,  328 

volatile  matter  in,  234,  235,  238,  239 

-washing,  243 

watering,  160 

water  from,  262 
Coal  Gas  {see  under  Gas) 
Cobb,    Prof.    J.    W.,    on    carbonization,    95, 

271 
Cobb  and  Rollings,  on  ammonia,  259 

on  cyanogen  yield,  260 

decomposition  of  hydrocarbons,  271 


Cobb  and  Rollings,    on    thermal    phenomena 

of  carbonization,  94 
Cockey's  washer,  335 
Coke,  ash  in,  263 

coke-oven,  1£2,  258 

composition  of,  263,  275 

conveyors  for  hot,  213 

economy  of,  in  settings,  93 

effect  of  heavy  charges  on,  281 

effect  of  oxygen  in  coal  on,  238 

friction  of  in  retorts,  147 

from  vertical  retorts,  283 

gas  obtained  from,  283,  284 

loss  of  heat  in  hot,  94,  101 

made  for  sale,  47,  93 

methods  of  quenching,  128 

nitrogen  in,  258 

oxygen  in,  263 

passage  of  gas  through  hot,  267 

space  occupied  by,  13,  54,  240 

steam,  raising  by,  507 

sulphur  in,  263 

"tacky",  98 

theory  of  combustion  of,  47 

used  for  carbonizing,  47,  62,  77,  93, 94, 126 
for  water  gas,  493 

volatile  matter  in,  279,  283 

yield  from  coal,  238 
Coke-ovens,  at  Birmingham,  78 

coke  from,  122,  258 

gas  from,  120 

Koppers',  120,  129 

weight  of  coal  charge  in,  279 
Colman,  H.  G.,  on  carbonization,  256,  280 

on  condensation,  297 

on  passage  of  gas  in  "  verticals  ",  284 
Colson  on  naphthalene  removal,  303 
Combustion,  chamber  design,  72,  73,  151,  152 

spontaneous,  of  coal,  244 

temperature  of  chamber,  49 

theory  of,  47 
Company,  statutory,  4 

non-statutory,  4 

Concrete,  constituents  of,  34,  38,  39,  45 
Condensation  of  gas,  286 

aqueous   vapour   and,   292,  296 

Brunswick  system,  299 

Coknan  on,  297 

counter-current   principle,    299 

design  of  apparatus  for,  293 

effect  of  foul  main  on,  177,  178 
of  rapid,  297 
of  "  shock,"  296 
of  scrubbing  plant  on,  356 

expansion  in,  178 

oil-fog  and,  296 

preliminary,  177 

tar-spraying  process,  297 

temperature  drop  during,  297 


INDEX 


517 


Condensation  of  gas,  theory  of,  296 

yield  of  tar  during,  298 
Condensers,  286 

after  exhausters,  325 

annular  type,  286,  289 

atmospheric,  286,  287 

battery  type,  286,  288 

capacity  of,  13,  22,  177,  290,  291,  292 

Carpenter's,  293,  299 

counter-current,  299 

"  Cyclone  "  extractor,  298 

design  of,  293 

efficiency  of,  286,  292 

•horizontal  type,  286 

multitubular,  291 

pipe  area  exposed,  290 

tar  spray  for,  295 

vertical  type,  286,  288 

water-cooled,  286,  291,  293 

water-tube  type,  291 

upkeep  of,  292 
•Cones,  Seger,  136 
Constam  and  Kolbe  on  coal,  237 
•Consumers,  number  of,  9 
•Consumption,  from  slot  meter,  1 1 

of  gas  per  head,  8 

•Contamination  of  gas  in  holders,  465 
Continuous  hydraulic  main,  164 
Convection,  loss  by,  94 
Conveying  machinery,  204 

angle  of  slope  of,  206,  208 

band  type,  207,  208 

calculation  of  horse  power  for,  224 

capacity  of,  206,  207,  210,  213,  216 

cost  of,  21,  205,  222 

de   Brouwer,   206,  214 

Dempster's,  217 

Drake's,  217 

gravity  bucket,  209,  212,  213 

horse  power  required  for,  207,  210,  224 

hot-coke,  213 

push-plate,  211 

saving  effected  by,  205 

speed  of,  206,  207,  210,  212 

taking  up  slack  in,  205,  206 

telphers,  213,  217 

travel  ling -tray   type,   209 

West's,  215 

Zimmer  on,  206 
Cooper's   liming   process,   260 
Corrosion,  prevention  of,  45 

of  retorts,  148 

Corrugated  iron  buildings,  36 
Cort's  anti-dip,  169 
Cost  of  plant,  10,  19,  128,  463 

of  buildings,  38,  128 

of   carbonization,    102,    128 

of  foundations,  35,   39,   128 

of  gasholders,  463 


Cost   of  operating  "  verticals  ",  107,  128 

of  water  gas,  494 

per  mouthpiece,  19,  25,  26,  74 

per  ton  of  coal,  19,  25,  26,  74,  128 
Counter-current  in   condensation,  299 
Coze,  M.,  75 

"  Creeping  "  in  retorts,  76 
Crown  of  gasholders,  curbs  for,  441 

rise  of,  426 

stresses  in,  440 

support  for,  446 

Cups  and  grips  for  gasholders,  426,  444 
Cutting  heat,  73 
Cyanogen,  367 

amount  in  coal  gas,  331,  369 

amount  recovered   per   ton  of  coal,  372, 
374 

British  Cyanides  Co.'s  process,  370,  371 

Bueb's  process,  376 

Ciselet  and  Deguide's   process,  376 

Cobb  and  Rollings  on,  260 

conversion  into  ammonia,  378 

cost  of  recovery,  380 

Davis-Neill  process,  370,  375 

double  cyanides,  378 

formation  of  in  retort,  368 

form  in  which  present,  260,  368 

Foulis  process,  370 

hydrolysis  of,  378 

in  coal  gas,  367 

influence  of  temperature  on,  260 

in  liquor,  368 

in  spent  lime,  368 

in  spent  oxide,  368,  377 

polysulphide  process,  370,  372 

proportion  of  nitrogen  recovered  as,  257, 
368 

reaction  with  oxide  of  iron,  369 
^recovery  as  ferrocyanides,  368 
as  hydrocyanic  acid,  377 
as  prussiate  of  soda,  370 
as  sulphocyanide,  368 
from  spent  oxide,  377 

South  Metropolitan  Co.'s  process,  377, 379 

tests  for  in  coal  gas,  381 
washers  for  recovery  of,  341 

Wilton's   process,   370,   371 
"  Cyclone  "  tar  extractor,  298 


Darwen  ascension  pipe,  162 
Davidson,  R.  B.,  anti-dip,  168 

on  coal  gas,  276 

on  effect  of  nitrogen  and  oxygen,  394 

on  liquor  purification,  358 
Davis-Neill  cyanide  process,  370,  375 
de  Brouwer  conveyor,  206,  214 

capacity  of,  216 


518 


INDEX 


de  Brouwer  conveyor,  power  required  by,  225 
speed   of,  206,   212,   216 
pusher,  192 

stoking    machinery,     190 
coal  stop  for,  191, 
cost  of,  192,  195 
life  of  coal  belt  of,   185 
Degradation  of  gas,  101,  160,  161,  284 

of  hydrocarbons,  266,  270,  271,  276 
Dellwik  water  gas  plant,  481 
Dempster's  reverse  flow  valve,  395 

washer,  335 
Derbyshire  coal,  244 
Dessau    vertical    retorts,    12,    99,    100,    108, 

129,  283 

Deterioration    of   coal,   244 
Diffusion  of  gas,  in  holders,  93 

through   retort    walls,    141,  142 
Dillamore  tar  tower,  172 
Diluent  effect  of  air,  393 
Dinas  fireclay,  133,  351 
Dip  pipes,  159,  162 
joints  for,  162 
machining  flange  of,  163 
serrated  edge  for,  162 
turned  edge  for,  163 
Direct  current,  227 
Direct-fired  settings,  46,  51,  64 
air-supply  to,   55 
coke  used  as  fuel  in,  47 
steaming  fuel-bed,  55 
Discharging  machinery,  183 
Distribution  plant,  cost  of,  12,  26 
Distributors,  liquor,  352 
Doors  for  retorts,  156 
Drake's  regenerator,  68 

stoking  machinery,  195 
Draught,  promotion  of  by  chimney,  66 

regulation  of,  68,  84,  92,  97 
Dry  lutes  for  purifiers,  405,  406 
Dry  mains,  168 
Dry  purification,  of  gas,  383 

plant,  15,  383 
Durham  coal,  239 
Dynamos  in  gasworks,  228 

"  Eclipse  "  dry  lute,  407 
Edinburgh  vertical  retorts,  116 
Electrical  deposition  of  naph   thalene,  301 

of  tar,  300 

Electrical  plant  in  gasworks,  227 
calculation  of  size  of,  229 
direct  current  for,  227 
dynamos  for,  228 
motors  for,  230 
units  consumed,  230 
Elevators,  angle  of  slope  of,  206,  208 
band  type,  207 
calculation  of  horse  power  for,  224 


Elevators,  capacity  of,  206 
cost  of,  21,  205 
de  Brouwer,  206 
saving  with,  205 
speed  of,  206,  207 
taking  up  slack  in,  206 
Zimmer  on,  206,  207 
Elland  vertical  retorts,  100,  111 
Endothermic  reaction,  50,  95 
Endothermicity  of  carbonization,  95 
Equilibrium  pipe,  172 
Erection  of  gasworks,  choice  of  site  for,  6 

surrounding  property  and,  7 
Ethane,    candle   and    calorific  power  of,  267 
decomposition  of,  268,  270 
in  coal  gas,  255,  267 

Ethylene,  candle  and  calorific  power  of,  267 
decomposition  of,  268,  271 
in  coal  gas,  255,  267,  271 
Euchenes'  heat  balances,  94 
Evans,  E.  V.,  on  purification,  415 
Ewell  fireclay,  133,  152 
Excavations,  cost  of,   32,   35 

timbering  of,  31 
Exhausters,  305 

blades  and  capacity  of,  309,  310 

by-pass  governor  for,  313 

calculating  capacity  of,  318 

capacity  of,   13,   14,  22,  310,  318 

construction  of,  308 

cost  of,  14,  305 

driving  power  required  for,  14,  319 

functions  of,  306 

governors  for,  312 

Gwynne-Beale  type,  307 

history  of,  305 

impeller,  324 

increase  in  yield  derived  from,  305 

lubrication  of,  316 

methods  of  driving,  14,  310 

multiple-blade  types,  308 

over-exhausting,    effect    of,    276 

power  required  to  drive,  319 

precautions  with.  317 

prior  to  condensers,   325 

pulling -up  of,  166 

Bateau  fan,  323 

reciprocating,  307 

regulation   of   "draw,"   90,  306,  312 
rotary  types,  307 
size  of  works  employing,  305 
saving  effected  by,  306 
size  of,  310 

"  slip  "  with,  14,  308,  319 
speed  of,  312 

steadying  the  "  draw,"  90,  306,  312 
steam  consumption  of,  311 
steam-jet  type,  321 
throttle  governor  for,  315 


INDEX 


519 


Exhausters,  Turbo,  322 
Expanded  metal,  36,  45 
Expansion,  allowance  for  in  pipework,  178 

joint  for  foul  main,  178 

of  retort  bench,  163 
Expenditure,  capital,   10,  128 
Explosions    in   apparatus,   92 

in  retort  bench,  87 
External  producers,  77 


Fans  for  water  gas,  483,  488 

"  Fast "  fires,  84 

Feld  process,  362 

Feldspar,  130 

Ferric -ferrocyanide    in    oxide,  369 

"  Ferrox,"  386 

Fiddes-Aldridge   stoking  machinery,   196,  198 

Fireclays  (see  under  Refractory  Materials),  130 

Fixed  ammonia,  328,  332 

Flooding,  avoidance  of,  7 

Floors,  retort  house,  44 

cost  of,  45,  74 
Flue,  area  for  settings,  64 

main,  cost  of,  74 
Fluxing  iri  retort  settings,  153 

of  ash  in  producers,  98 

of  fireclays,  140,  148 
Formulae,  structural  chemical,  264 

various  gasworks,  9  to  17,  224,  401,  440, 

445 

Foster  on  nitrogen  recovered,  257 
Foulis  cyanide  process,  370 
Foul  main,  arrangement  of,  180 

construction  of,  178 

functions  of,  177 

joints  for,  160 

methods  of  supporting,  178 

rule  for  length  of,  291 
Foundations,  7,  30 

allowable  pressure  on  soils,  34 

concrete  for,  34 

controlling  water  in,  7,  31 

cost  of,  35,  39,  74,  128 

floating,  33 

for  vertical  retorts,  33 

grillage,  33 

materials  for,  34,  38,  39,  45 

pier,  32 

raft,  33 

sinking  of,  33 

subsoil  for,  7,  32 

trial  borings  for,  30 

various  types  used,  32 
Free  ammonia,  328,  332 

carbon,  270,  277,  280 
Free  space,  in  horizontal  retorts,  160 

G.  P.  Lswis  on,  281 

in  vertical  retorts,  105,  118 


Fuel  economy,  93,  101,  149 

consumption,  47,  62,  77,  94,  126,  281 

for  producers,  78 
Furnaces  (see  under  Producers) 
Furnace -charging  machine,!  203 
Fusibility  of  fireclays,   130,   140 


Ganister  clay,  133,  134 
Gas,  acts  governing  public  supply  of,  4,  6 
ammonia  in,  326,  330,  331 
coke-oven,  120 
composition  of,  276,  284,  496 

of  primary,  254 
condensation  of,  286 
consumption  of  per  head,  8 
degradation  of,  101,  160,   161,   266,  284 
effect  of  temperature  on,  266 
hydrocyanic  acid  in,  326,  331,  369 
make  per  ton  of  coal,  102,  110,  161,  166, 

179,  242,  274 
Mond,  78,  80,  96 
multiple,  242 
origin  of  word,  1 
producer,  composition  of,  49 
public  supply  of,  4 
specific  gravity  of,  7 
sulphur  compounds  in,  331,  383,  397,399, 

413,  467 
sulphuretted  hydrogen  in,  326,  331,  383, 

495 

unaccounted  for,  9 
yield  from  coke,  283 

from  tar,  277 

per  retort,  128 

per  unit  of  ground  area,  128 
Gasholders,  420 

addition    of  outer  lift  to  existing,  421 

bottom  curbs  of,  441 

brickwork  tanks  for,  454 

calculation   of  capacity  of,  425 

compression  in  top  curb  of,  442 

contamination  of  gas  in,  465 

cost  of,  463,  464 

Cripps'   fluted   tank,   462 

crown -rest  framing  for,  433 

cups  and  grips,  426,  444 

curbs  for  tanks,  458 

design  of,  424 

of  tanks,  457 
diffusion  of  gas  in,  93 
East  Greenwich,  464 
failure,  means  of,  428 
function  of  water  in  tank,  422 
guide-framing  of,  427 
guide  rollers  for,  427 
lifts,  depth  of,  426 
New  York,  459 
Nuremberg,  423 


520 


INDEX 


Gasholders,  position  of.  18 

pressure  thrown  by,  465 

proportions  of,  17,  424 

requisite  capacity  of,  420 

rise  of  crown  of,  426 

riveted  joints  in  tanks,  460 

shear  in  standards  of,  436 

snow  pressure  on  bell    of,  429 

spiral  type,  423,  449 

standards  for,  434 

steel  tanks  for,  457 

stresses  in  bell  of,  440 
in  guide-framing  of,  428 
in  tanks  of,  455 

struts,  design  of,  439 

sulphuretted  hydrogen,  stains  from,    397 

tanks  with  bulging  sides,  461 

Tegel,  447 

ties,  design  of,  439 

various  forms  of,  422 

wind  pressure  on,  428 

wire-cable  type,  423 
Gaslight  and  Coke  Company,  2,  4,  11 
Gasworks,  buildings  for,  35,  128 

capacity,  12,  128 

capital  expenditure  on,   10,  26,  128 

comparative  cost  of  buildings  for,  35,  128 

cost  of  plant,  12, 19, 26,  128,  409,  413,  494 

erection  of,  6 

land  required,  8,  128 

size  of  mains,  18 
of  plant,  8 

surrounding  property  and,  7 
Generator  settings,  construction  of,  -56,  64,  66 

fuel  used  in,  47 
German  retorts,  144,  149 
Gill's  clinkering  machine,  202 

furnace -charging  machine,  203 
Glasgow  vertical  retorts,  100,  114,  129 
Glazing  for  retorts,  142 
Glover,  Thos.,  on  chamber  retorts,  126 

on  grate  area,  64 

on  scrubbers,  350,  356 
Glover- West   vertical  retorts,  12,  98,  99,  100, 

103,  107,  128,  283 

Gold,   recovery   by   means   of  cyanogen,    367 
Goulden,  Thos.,  on  gas  yields,  274 
Governors,  arrangement  of  retort  house,  74, 
90,  174,  178,  180 

for  exhausters,  312 

size  of,  16,  23 
Graphite,  235 
Grate  area,  effect  of  large,  98 

for  producers,  63,  97 

for  verticals,  105,  108,  111,  116 
Gravity  bucket,  209,  212 
Green's  purifiers,  400 
Grids  for  purifiers,  408 
Grillage  foundation,  33 


"  Grog  "  in  fireclay,  132 

Ground  area  required  for  retort  benches,  101, 

111,  128 

for  water  gas  plant,  466 
Ground  level,  7 

Guest-Gibbons  stoking  machinery,  200 
Guide-framing    of   gasholders,  427 
Gwynne-Beale  exhauster,  307 


Hand-made  retorts,  144 
Haug,  on  condensers,  292 
Heat,  balance  in  setting,  93,  94 

in  water  gas  plant,  499 

control  of  in  setting,  92 

cutting,  73,  140,  152 

distribution  of  in  settings,  72,  94 

expenditure  on  carbonization ,  94 

local,  72,  73,  146 

losses,  curtailment  of,  55,  62,  96,  101,  154 

lost  in  hot  coke,  94,  101 

producer  losses,  82 
Heavy  charges  in  retort,  amount  of  coal  with, 

281 

effect  on  temperature,   282 
influence  on  ammonia,  259 
influence  on  tar,  269 
merits  of,  281 
Helps'  anti-dip,  169 
Herring's  rule  for  chimnej^  area,  64 
Hirsch's  furnace,  135 
Holders  (see  Gasholders),  420 
Rollings  on  carbonization,  95 
Holmes-Winstanley  vertical  retorts,  101,  118 
Horizontal  retort   bench     (see    under    Retort 
Settings),  46,  128 

condenser,  287 

Horse-power,    calculation    of    for    conveyors, 
etc.,  224 

for  vertical  retorts,  106,  108 

required  for  conveyors,  207,  210 
for  exhausters,  319 
for  washer-scrubbers,  346 
Hot-coke  conveyors,  214 
Hot  purification,  413,  414 
Houses,  retort,  20 

Humphreys  and  Glasgow  water  gas  plant,  472 
Humus  bodies  in  coal,  235,  236,  254 
Hunt's  rule  for  purifiers,  15,  401 
Hunter-Barnett    pusher,    187,  188 
Hurdle  grids  for  purifiers,  408 
"  Hurricane  "    Tar    extractor,  496 
Hydraulic  main,  163 

agitators  for,  176 

ammonium  chloride  in,  176 

construction   of,    163 

continuous  type,  164 

functions  of,  166 

gas-take-off  from,  164,  166 


INDEX 


521 


Hydraulic  main,   Langford's  arrangement  of, 
181 

method  of  supporting,  166 

pitching-up  of,  175 

seal  in,  167,  177,  275 

temperature  of,  297 
Hydrocarbons,  acetylene  series,  264 

affinity  of  tar  for,  297 

aromatic  series,  264,  267,  297 

benzene  series,  264 

Berthelot's  theory  of,  268 

Bone's  theory  of,  270 

candle  and  calorific  power  of,  267 

CH  and  CH2  residues,    270 

Chemistry  of,  263 

Cobb's  theory  of,  271 

effect  of  bonds  on  stability  of,  269 

homologous  series  of,  264 

in  coal,  235,  236,  254 

Lewes  on,  268 

liquefiable,  292 

olefine  series,  264 

paraffin  series,  237,  264 

retention  of,  in  gas,  297 

saturated,  in  gas,  256 

splittiiig-upof,  101, 160, 161,  266,  270,  271 

unsaturated  in  gas,  237,  256,  276 

Wheeler  and  Burgess  on,  271 
Hydrocyanic  acid  in  coal  gas  (see  under  Cy- 
anogen), 326,  331,  367,  369,  383,  384 
Hydrogen,  from  degradation  of  hydrocarbons, 
270    273 

in  coal,  234,  238,  239,  255,  261 

in  coal  gas,  254,  255,  275 

in  coke,  255,  263 

in  producer  gas.  49,  81 

in  water  gas,  495,  496 

unoxidized,  237 
Hydrolysis,  378 


Illuminating  power,  reduction  of  by  solvents, 
302,  303 

regulation  of,  91 
Impurities,  in  coal  gas,  326,  333 

in  fire-clays,  131,  132,  140,   148 

in  gas  at  condensers,  331 

in  gas  as  distributed,  384 

in  gas  at  purifiers,  383 

in  water  gas,  466 
Inclined  retort  settings,  75 

cost  of,  77 

fuel  used  by,  77 
Inclined  chamber  ovens,  124 
Insulation  of  retort  bench,  62,  161 
Intensity,  calorific,  49 
Intermittent,  vertical  retorts,  12,  99,  100,  108, 

129 
Iron  dust,    effect    of  in    producers,  140 


Jenkins-de-Brouwer  machinery,  192 
Jet-photometer,  91 
"  Joint  Board  "  supply  of  gas,  5 
Joints,  ascension  pipe,  159 

dip-pipe,  162 

dry  purifiers,  405 

expansion,  178 

for  foul  main,  160 

for  mouthpieces,  157 

for  purifier  plates,  402 

in  cast-iron  work,  348 

rust,  348 

temporary,  for  bridge-pipe,   163 


"  K  and  A  "  Water  Gas  plant,  478 
Kaolin,  130,  131 
Kent's  steam  meter,  487 
Kerpely  producer,  78,  81 
Klonne  regenerator,  68 
Koppers'  chamber  ovens,  120,  129 
direct  recovery  process,  364 


Labour   costs,   for   carbonization,  182 

for  horizontal  retorts,   128,  204 

for  vertical  retorts,  101,  128 

for  water  gas,  494 

saving  of  with  machinery,  183,  204 
Laming's  mass,  386 

process,  357 
Lamps,  public,  26,  27 
Lancashire  coal,  239 
Land,  amount  required,  8,  10,  12,  128,  466 

cost  of,  12 

Langford's  hydraulic  main  arrangement,  181 
Leather's  naphthalene  process,  303 
Lebon,  Phillipe,  1 
Lessing  R.,  coal  test,  241 
Level  of  site,  7 

water,  7,  31,  41,  42 

Lswes,  Prof.  V.  B.,  94,  268,  269,  276 
Lewis,    G.  P.    on    retort    temperatures,  282 
Leybold,  369 

Lifting  gear  for  purifiers,  408 
Lifts,  depth  of  gasholder,  426 
Lighting,  public,  26,  27 
Lignite,  233,  234,  235,  237 
Lime,    amount  required  for  purification,    413 

bond  in  fireclays,  149 

compounds  in  fireclays,  131,  133,  134 

cyanide  compounds  in  spent,  368 

effect  of  in  oxide  boxes,  370 

purification  for  sulphur  compounds,  347 

reaction  with  SH2,  398 
with  CS2,  398  ' 

space  occupied  by,  240 
Liming  of  coal,  413,  417 


522 


INDEX 


Liquor,  ammonia  in,  330,  332 

carbon  dioxide  in,  330 

composition  of,  327 

cyanide,  372,  374 

cyanogen  in  spent,  368 

distillation  of,  329 

distributors  for  scrubbers,  352 

from  hydraulic  main,  330 

means  of  taking  off  from  hydyraulic,  170 

oscillation  of  in  hydraulic,  164 

oxidation  of,  1529 

purification,  357 

sulphur  in,  330,  331 

sulphuretted  hydrogen  in,  330 
Livesey  washer,  334,  354 

manlid,  453 
Load  curve,  420 

Local  Authority  as  gas  supplier,  5 
Local  heating,  72,  73 
Love's  inclined  retorts,  76 
Lunge,  on  gas  liquor,  332 
"  Lux  "  purifying  material,  386 


Machine-made  retorts,  144 
Machinery  in  gasworks,  21,   182 
Magnesia  in  fireclays,  133 

melting  point  of,  155 
Mahler  on  carbonization,  96 
Mains,  cost  of,  25,  26,  28 

foul,  177 

hydraulic,  163 

size  of,  18 
Make  per  ton,  102,  110,  161,  166,  179,  242 

ascension  pipes  and,  161 

considerations  affecting,  242,  274 

effect  of  decomposition  on,  272,  276 

effect  of  vacuum  on,  179 

gas  multiple,  242 

increased  by  steaming,  110,  285 

Meunier's  floats  and,  166 

with  verticals,  102,  110 
"  Manual  "  stoker,  182 
Manufacturing  costs,  102,  128 
Maximum  day,  10 

Mechanical   handling    of    materials,  182 
Mekers  furnace,  135,  138 
Mellor,  Dr.  J.  W.,  137 
Melting  point  of  refractories,  155 
Merrifield-Westcott-Pearson   water  gas  plant, 

476 
Meters,  slot,  11 

station,  23,  26 
Methane,    calorific    power   of,  267,  268 

decomposition  of,  267,  268 

illuminating  power  of,  267 

in  coal  gas,  254,  255,  275,  276 

in  producer  gas,  49 

in  water  gas,  6,  495,  496 


Methane,  Lewes'  research  on,  268 

series  of  hydrocarbons,  246 

structural  formula  of.  265 
Methane -hydrogen  plant,  470,  501 
Metropolitan  Gas  Acts,  4 
Meunier's  floats,  165 
Meyer  and  Hempel  on  liquor,  332 
Milbourne's  dry  lute,  407 

rule  for  purifiers,  403 

valve,  395 

Mond  producer  and  recovery  plant,  78, 
ammonia  from,  257,   259 
sulphate  from,  257 
Mond  gas,  calorific  power  of,  80 

composition  of,  496 

cost  of,  80 
Motors,  electric,  230 
Mouthpiece,  attachment  of,  157 

bracing  for,  158 

cost  per,  19,  74 

for  retorts,  156 

make  per,  13,  19,  128 

self -sealing,  156 

shield  for,  191 
Multiple,  gas-,  242 
Multi tubular  condenser,  291 
Munich  chambers,  98,  129,  147 
Murdoch,  John,  1 


Naphthalene,  301 

abrupt  condensation  for,  303 

anthracene  oil  for,  301 

Botley's  process  for,  303 

Bremond  on,  303 

Brunswick  washing  process,  299 

Butterfield  on,  302 

carburetted  water  gas  and,  304,  467 

Colson's  process  for,  303 

effect  of  "  Cyclone  "  extractor  on,  298: 
of  freespace  on,  280 

electrical  process  for,  301 

Ferguson   Bell's   method,  303 

formation  of  from  benzene,  280 

Leather's  process  for,  303 

methods  of  removing,  301 

Meunier's  floats  and,  166 

naphtha  washing  for,  303 

paraffin  for,  301 

quantity  in  gas,  297,  302,  331 

reduced  by  tar  spray,  295 

stoppages  from,  286 

structural  formula   of,  265,  280 

tar  washing  for,  299,  303 

vertical  retorts  and,  277 

water-gas  tar  for,  301,  302 
Naphthenes  in  coal  gas,  267 
Neat  oxygen  water  gas  process,  469* 
Nicol,  E.  W.  on  boiler  fuels,  511 


INDEX 


523 


Nitrogen,  distribution  of  in  coal,  256,  262 
effect  of  on  candle  and  calorific  power,  276, 
394 

in  coal,  234,  238,  239,  256 

in  coal  gas,  275,  276,  278,  279 

in  coke,  257,  258,  263 

in  water  gas,  496 

tar,  258 

Non-conducting  material  for  retort  bench,  62 
Non-statutory  company,  4 

rights  of,  5 

Norwich  chamber  retorts,  126 
"  Nostrils,"  design  of,  72,  73 
Nottinghamshire  coal,  239 


Oil,  fog,  296,  298 

used  in  manufacture  of  water  gas,  493 
Olefine  hydrocarbons,  264 
Oregon  process  for  sulphur  purification,  413, 

414 
Oscillation  of  liquor  in  hydraulic  main,  164 

prevention   of  by  anti-dip,  168 

by  Meunier's  floats,  165 
Oughtibridge  clay,  133,  134,  147 
Outside  producers,  77,  117 
Overcracking  of  gas,  101,  266,  267,  269,  275, 

279 

Oxidation  of  gas  liquor,  329 
Oxide  of  iron,  addition  of  sawdust  to,  396 

alumina  in,  385 

ammonia,  effect  of  on,  15,  391,  396 

amount  required  for  purification,  413 

analysis  of,  385 

back-pressure  from,  394 

basis  of  selling  spent,  387 

Belgian,  240 

caking,  prevention  of,  396 

depth  of  tiers,  391 

Dutch,  240 

effect  of  air  on,  391 
of  cyanogen  on,  369 
of  heating,  395 

ferric  oxide  in,  384,  387 

form  of  tender  for,  387 

in  fireclays,  133 

inert  matter  in,  384 

merits  of  powdered,  396 

moisture  in,  385,  387,  394 

natural,  384 

oxidation  of,  385 

prepared,  240,  386 

reactions  with  SH2,  385 

removal  of  SH2  by  means  of,  384 

revivification  of,  385 

silica  in,  385 

space  occupied  by,  240 

spent,  385 


Oxide  of  iron,  sulphur  in  spent,  385,  396 

water  of  combination  in,  385 

when  acid,  391,  396 

work  done  by,  15,  16,  413 
Oxidizing  flame,  140 
Oxygen  in  coal,  234,  237,  238,  239,  262 

occluded,  246 
Oxygen  absorbed  in  dry  purifiers,  392 

distribution  of,  262 

effect  of  on  candle  and  calorific  power,  276,. 
393 

in  coke,  263 

in  purification,  275,  392 


Paraffin  as  a  naphthalene  solvent,  301 

hydrocarbons,  237,  255,  264,  271 
j  Parkinson's  retort  house  governor,  180 
!  Parliament,  application  to,  5 
Peat,  235 

Perkin,  Sir  Wm-,  3 
Phenols  in  gas  liquor,  328 
Photometer,  jet-,  use  of,  91 
Pier  foundations,  32 

walls,  58 

Pipes,  ascension,  bridge  and  dip,  159 
joints  for,  157, 159, 160, 162,  163 

loss  of  heat  through,  94 

stopped,  160,  329 
Pitch  in  water-gas  tar,  497 
Plant,  arrangement  of,  18 

cost  of,  10,  19,  35,  38,  74,  102,  128,  463^ 
494 

distribution,  12 

mechanical,  21,  182 

poVer,  22,  182 

retort-house,  128 

size  of,  12,  128 

sulphate,  17,  24 

Plates,  size  of  cast  iron,  348,  402 
Pollution  of  water  supply,  8 

of  water  in  gasholders,  465 
Polymerization  of  acetylene,  269 
Polysulphide  cyanide  process,  370,  372, 380 
Poole's  heat  balance,  94 
Porosity  of  fireclays,  135, 138,  154 
Porosometer  for  fireclays,  138 
Power,  cost  of  for  vertical  retorts,  107 

required  for  vertical  retorts,  107,  108 

for  conveyors,  etc.,  207,  210,  224 
Prepayment  installation,  cost  of,  11 

consumption  from.  11,  26,  27 
Pressure,  conditions  throughout  works,  307 

loss  of,  due  to  elevation,  7 

on  purifier  covers,  408 

on  various  soils,  34 

thrown  by  gasholder,  465 
Primary  air,  63,  66,  84,  97 
Producers,  46 


524 


INDEX 


Producers,  air  supply  to,  42,  49,  84 
bracing  for,  156 
calorific  power  of,  gas,  81 
chimney  area  for,  64 
coke  used  in,  47,  62,  77,  93,  94,  126 
construction  of,  62,  154 
correct  shape  for,  62 
cost  of.  74 
depth  of  fuel  in,  56 
effect  of  steam  in,  50.  Ill,  1J8 
equations  for  formation  of  gas,  50 
explosion  of  gas  in,  87 
fast  fires  in,  84 
gas,  composition  of,  49,  81 
grate  area  for,  63,  128 
heat  losses  with,  82 
high-pressure,  77 
Kerpely,  78,  81 
lining  of,  56,  63,  154 
Mond,  78,  96,  496 
outside,  67 

regulation  of,  83,  92,  97 
single  type,  56,  62 
slow  fires  for,  83 
stepped  grate  for,  108,  111,  112 
temperature  cf,  49 
testing  gases  frcm,  86 
Projectors  for  coal,  190,  195 
Protection  for  retorts,  149 
Provan  works,  producers  at,  77 
Provisional  order,  4 
Proximate  analysis  of  coal,  241 
Prussian  blue  in  spent  oxide,  368,  369 
Prussiate  of  soda,  368,  370 
Public  lighting,  26,  27 
Purchase  clause,  5 
compulsory,  6 

of  undertaking,  5,  6 
Purifiers,  admission  of  air  to,  391 
admission  of  steam  to,  369,  395 

area  required,  15,  23 

"  Bearscot  "  valves  for,  412 

buildings  for,  410 

catch  boxes,  386,  390,  391 

centre  valves  for,  410 

connections,  rule  for  size  of,  403 

construction  of,  388 

cost  of,  12,  15,  409,  413 

covers  for,  404,  409 

cover  fastenings  for,  405 

depth  of  material  in,  391 

dry  lutes  for,  405,  406 

no.T  plates  for,  404 

general  notes  on,  404 

Green's  type,  400 

in  rotation  and  series,  388,  389 

joints  for  plates  of,  402 

lifting-gear  for,  408,  409 

method  of  operating,  390 


Purifiers,  oxygen  absorbed  in,  392 
pressure  on  covers  of,  408 
pressure  thrown   by,  307,  394 
rule  for  depth  of,  403 
size  of,  16,  401,  402 
steam  coils  in,  396 
thickness  of  plates  for,  402 
tier  valves  for,  405 
valves  for,  410 
water  valves  for,  412 
Week's  valves  for,  413 
Purification  of  coal  gas,  326,  383 
admission  of  air,  391 
alternate  flow  in,  394 
backward  rotation,  390 
Beckton  lime  method,  398 
"  Brownox  "  for,  386 
by  amino  compounds,  413,  417 
by  liquor,  357 
by  sulphided  lime,  397,  413 
Burkheiser  process,  360 
Carpenter-Evans  process,  413,  414 
Davidson  on,  394 
diluent  effect  of  air,  393 
effect  of  ammonia  on,  369.  393 

of  cyanogen  on,  369 

of  lime  on  oxide,  370 

of  Prussian  Blue  on,  369 

of  steam  on,  369,  395 
emergencies  in,  397 
excess  of  air  and,  393 
"  Ferrox  "  for,  386 
of  coal  gas,  hot  methods  of,  397 
lime,  397 
"  Lux  "  for,  386 
material  required  for,  413 

too  dry  in,  394 

Oregon  process,  413,  414 
oxide  of  iron  for,  385 
oxygen  absorbed  during,  392 

reactions  during.  385 
removal  of  sulphur  compounds,  413 
revivification  in  situ,  391 
water  required  for,  333 
Weldon  mud  for,  386 
Wurtz  on,  394 
Push-plate  conveyor,  209 
Pyridine,  as  a  coal  solvent,  233 

in  tar,  258 
Pyrites  in  coal,  243,  261 

Quartz  in  fireclays,  131 

Radiant  heat,  effect  on  gaseous  products,  267, 
272,  280 

selective  action  of,  296 
Radiation,  loss  of  heat  by,  55,  94 

prevention  of  heat  loss  by,  62,  63 


INDEX 


525 


Raft  foundation,  33 

Railway  sidings  for  gasworks,  7 

Rankine's  formula  for  pressure  on  walls,  40 

"  Rapid  "  stoker,  182 

Rateau  fan  for  exhausting,  323 

for  water  gas  blast,  482 
Reducing  flame,  140 
Refractory  materials,  130 

aluminous  types,  133 

analyses  of  various,  131,  133 

chamotte  for,  132 

classification  of,  133 

contraction  and   expansion  of,   135,  138, 
149, 151 

corrosion  of,  148 

cost  of:  148 

Dinas  clay,  133,  151 

Ewell  clay,  133,  152 

fluxing  of,  140,  148,  150 

furnaces  for  testing,  135, 138 

fusibility  of,  131   140,  145,  155 

Ganister  clay,  133,  134,  153 

glazing  for  retorts,  142 

"grog"  for,  132 

heat  conductivity  of,  140,  141,  149 

materials,    impurities  in,   131,   132,  140, 
148,  153  *  .- 

insulating  material,  140 

iron  compounds  in,  133,  134 

kaolin,  130,  131 

life  of  retorts,  141,  146,  147,  149 

lime  bond  in,  149 

magnesia  in,  133,  134 

melting  points  of  various,  155 

origin  of,  130 

Oughtibridge  clay,  133,  134,  147 

porosity  of,   135,  138,  141,  145,  154 

preparation  of,  131 

quartz  in,  131 

reducing  flame  and,  140 

refractoriness  of,  135 

retort-making  machine,  145 

segmental  retorts,  145,  149 

silica  retorts,  149 

shrinkage  of,  132 

siliceous  clay,  133 

Stourbridge  clay,  132,  133 

tests  for,  135 

titanic  oxide  in,  133,  134 
Regeneration,  effect  of,  50,  97,  98 
Regenerators,  66 

Brooke's,  70 

Brown's,  70 

construction  of,  67,  154 

Drake's,  68 

Elland,  114 

Gibbons  and  Masters',  68 

Glover-West,  107 

heat  saved  by,  94 


Regenerators,  Klonne  brick,  68 

Pintsch's,  69 

short  circuiting  in,  68 

Winstanley's,  71 
,Woodall-Duckham,  98 
Reinforcement,  for  foundations,  32 

for  gasholder  tanks,  453 

for  walls,  38,  39 

Resin     bodies,     effect     of,     on     spontaneous 
combustion,  246 

in  coal,  235,  236 

products  yielded  by,  254 
Retort  house,  comparative  costs  of,  21 ,  38,  74, 
128 

dimensions  of,  20 

floors  for,  44,  74 

governors,  74,  90,  174,  178,  180 

foundations  for,  32 

labour  costs  in,  204 

machinery,  181 

roofs,  41,  44 

stage  house,  41 

subway  house,  41 
Retorts,  carbon  deposit  in,  144 

capacity  of  various,  12,  128,  281 

chamber,  120,  129 

corrosion  of,  148 

cost  of,  128,  148 

cost  per  mouthpiece,  19 

demands  made  upon,  141 

Dessau,  12,  99,  100, 108,  129 

diffusion  of  gas  through,  141,  142,  146 

Elland,  101,  111 

expansion  of,  149 

free  space  in,  105,  118.  160 

German,  141,  149 

Glasgow,  101,  114,  129 

glazed,  142 

Glenboig,  153 

Glover-West,  12,  98,  99, 100,  103,  128 

hand  and  machinemade,  144 

Herring's,  101,  116,  129 

Holmes-Winstanley,  101,  118 

horizontal,  46 

intermittent,  12,  99,  100,  108,  129 

life  of  141,  146,  147,  149 

make  per  mouthpiece,  13,  19,  128 

manufacture  of,  140,  144 

mechanical  strength  of,  141 

mouthpieces  for,  148,  157 

porosity  of,  141.  145 

protection  for,  149 

segmental,  145,  149 

shape  of  various,  128 

shield  blocks  for,  150 

silica,  149 

stop-ended,  12,  52 

temperature  of,  49,  118 
"  through  ",  12 


526 


INDEX 


Retorts,  vertical,  12,  100,  128 

Woodall-Duckham,  12,  64,  98,  100,  128 

wooden  shuttering  for,  150 
Retort  Settings,  bracing  for,  156 

capacity  per  unit  of  ground  area,  72,  73, 
128 

chamber  ovens.  120,  128 

chimney  area  for,  64 

combustion  chambers  of,  151 

construction  of  regenerators,  67,  154 

control  of,  83,  92 

cost  of,  74,  102,  128 

cross  walls  of,  151,  152,  153 

cutting  heat  in,  73,  140,  152 

dimensions  of,  53, 128, 281 

direct-fired,  46,  51 

explosions  in,  87 

fittings  for,  156 

fluxing  in,  140, 148, 150,  153 

fuel  required  for,  47,  62,  77,  93,  94,  281 

gaseous-fired,  46,  48,  66 

generative,  56,  64,  66 

grate  area  for,  63,  105,  108,  111 

heat  losses  in,  94 

horizontal,  46,  128 

inclined,  75,  77,  124 

local  heating  in,  72,  73,  146 

main  arches  of,  54,  58,  60,  62 

Norwich  Chambers,  126 

operation  of,  63 

outside  walls  of,  154 

preventing  heat  losses  in,  55,  62,  96,  101, 
154 

refractory  materials  for,  139 

regenerative,  56,  66,  96 

semi-gaseous,  46,  50,  52 

stopping  temporarily,  89 

Sunday  stopping,  89 

temperature  of,  49,  50,  97,  98,  118,  140, 
281 

thermal  balance  of,  94 

types  of  regenerators,  66 

vertical,  100,  128 
Reverse  action  in  purifiers,  394 
Revivification  of  spent  oxide,  385 

in  situ,  391 

Rincker-Wolter  water  gas  plant,  504 
Roofs  for  retort  house,  41,  44 

covering  for,  44 
Rotation  system  of  purification,  390 

backward,  390 

forward,  391 

Sale  of  gas,  estimating,  9 
Saturated  hydrocarbons,  263 
Scotch  coals,  239 
Scrubbers,  Barker's  mill  for,  352 

capacity  of,  15,  22,  355 

cast-iron   plates   for,    348 


Scrubbers,  clean  water,  333,  350 

construction  of,  348 

contact  time  in,  355 

diameter  and  height  of,  348 

effect  of  condensers  on,  356 

Glover's  system  of,  350 

guarding  against  back-pressure  in,  349 

liquor  distributors  for,  352 

loss  of  ammonia  in,  357 

packing  for,  349 

pressure  thrown  by,  307 

size  of,  355 

of  boards  for.  349 

tar  in,  297 

tower,  15 

tumblers  for,  352 

types  of,  333 

water  required  for,  356 
Scurf  in  retorts,  144,  255,  281 
Scurfing,  allowance  for,   19 
period  of,  107 

with  vertical  retorts,  107,  114 
Seal  on  dip-pipes,  167,  177,  275,  306 

breaking  of,  167 

conditions  governing  retention  of,  167 

dispensing  with,  168 

equalization  of,  163 
Secondary  air  amount  required,  50 

direction  of,  99 

regeneration  of,  66 

regulation  of,  68,  73,  84,  140 

temperature  of,  50 

when  starting  up,  84 
Seger  cones,  136 
Segmental  retorts,  145 

cost  of,  149 

life  of,  149 

saving  with,  146 
Semi -gaseous  settings,  46,  52 
Services,  cost  of,  26,  28 
Settle-Padfield  retorts,  101 
Shafts,  chimney,  64 
Shear  in  gasholder  standards,  436 
Shirley,  Thomas,  1 

Short  on  distribution  of  nitrogen  in  coal,  257 
Shrinkage  of  fireclays,  132 
Silica  in  fireclays,  130, 133, 148 

in  oxide  of  iron,  385 

shield  blocks,  150 

retorts,  149 
Siliceous  fireclays,  133 
Simmersbach  on  carbonization,  279 
Single  ascension  pipe,  161 
Site,  choice  of  a,  6,  18,  30 

shape  of,  8 
Slag-wool  joint,  163 
Sliding-scale,  4 
"  Slip,"  in  exhausters,  14,  308,  319 

in  producers,  97 


INDEX 


527 


"Slot  meter,  consumption  through,  11,  26 

cost  of  installation,  11,  26 
'Slow  fires,  83 
Smith  and  Pearson's  hydraulic  main  arrange- 
ment, 176 

Snow  pressure  on  gasholders..  429 
Sodium  cyanide,  368 
Soils,  pressure  allowed  on  various,  34 
'Solvents  for  coal,  233 
South  Metropolitan  Gas  Co.,  11,  17,  18 

cyanide  process  of,  377,  379 
Space  occupied  by  various  materials,  13,  240 
Spandrils  of  main  arches,  60,  62,  74 
Specific  gravity  of  coals,  234 
of  coal  gas,  7 
of  water  gas,  7 

Speed  of  conveyors,  206,  207,210,212,213,216 
of  elevators,  206,  207 
of  exhausters,  312 
:Spent  oxide,  basis  of  selling,  387 
cyanogen  in,  368 
formation  of,  385 
prussian  blue  in,  369 
revivification  of,  385 
sulphur  in,  386 
Sperm  per  ton  of  coal,  241 
Spiral  guided  gasholders,  423,  449 
Spontaneous  combustion  of  coal,  244 

means  of  preventing,  246 
Stage  retort  house,  41,  43,  48 
Station  meters,  23,  26 
Statutory  company,  4 
Steam,  admission  to  purifiers,  369 
coals,  233,  234,  235,  238 
generation  on  gasworks,  507 
-jet  exhausters,  321 
-meters  for  water  gas,  487 
Steam  supply  to  producer,  50,  55,  111,  118 

to  retorts,  110,  275,  285 
used  for  making  water  gas,  493 
Stoking  machinery,  various  forms  of,  182 
electrical  plant  for,  227 
operating  costs  of,  185 
Stop-ended  retorts,  12,  46,  51,  52,  56 
Stopped  pipes,  160,  161,  163,  281,  329 
Stopping  gasmaking  temporarily,  89 
Storage  of  coal,  13,  20,  244,  250 
design  of  stores,  39 
deterioration  due  to,  244,  249 
spontaneous  combustion  and,  244 
Storage  of  Gas  (see  Gasholders)  420 
amount  required,  16,  17,  23,  420 
ground  required  for,  17 
methods  of  increasing,  17 
Stourbridge  clay,  132 
Struts,  design  of  gasholder,  439 
Sub-way,  retort  house,  41,  43 
Sulphate  of  ammonia,  Burkheiser  process  for, 
362 


Sulphate  of  armmonia,  Feld  process  for,  362 
increased  by  liming,  260,  379 

by  steaming,  261 
plant,  17,  24 

recovery  by  "  direct "  methods.  359 
space  occupied  by,  240 
yield  per  ton  of  coal,  257,  258,  381 

with  Mond  plant,  257 
Sulphates  in   fireclays,    134 
Sulphided  lime,  purification  with,  399,  413 
Sulphocyanide,  recovery  of,  258,  368 
Sulphur  clauses,  383,  384 

distribution  of  in  coal,  262 
effect  of  heavy  charges  on,  281 
in  coal,  238,  239,  261 
in  coke,  263 
in  gas  liquor,  330,  331 
in  spent  oxide,  386 
Sulphur  compounds  in  gas,  261,  331,  383,  384, 

397,  399,  413,  467 
absorption    of    by  liquor,    331 
reaction  with  lime,  399 
removal  by  Brunswick  process,  299 
by  alkalinated  cellulose,  413,  418 
by  "  Athion  "  process,  413,  418 
by  amino  compounds,  413 
by  Carpenter-Evans  process,  413 
by  liming  of  coal,  413 
by  Oregon  process,  413 
Sulphuretted  hydrogen,  in  coal   gas,  326,  331, 

383,  384 

in  gas  liquor,  330 
in  water  gas,  495 
reaction  with  ammonia,  327 
with  lime,  398 
with  oxide  of  iron,  385 
stains   from  gasholder,   397 


Tanks  for  gasholders,  453 

bottom  curbs  for,  458 

bulging  sides  for,  461 

cost  of,  463,  464 

Cripps'  fluted  type,  462 

design  of,  457 

efficiency  of  joints  of,  460 

riveted  joints  for,  461 

steel,  457 

stresses  in,  454 

thickness  of  side  plates  for,  460 

top  curbs  for,  459 

various  types  of,  453 
Tar,  affinity  of  for  hydrocarbons,  297 

amount  of  gas  yielded  by,  277 

as  a  naphthalene  solvent,    299,  301,  302, 
303 

-box,  170 

Brunswick  washing  system,  299 

cannel-,  240 


528 


INDEX 


Tar,  effect  of  heavy  charges  on,  281 
of  on  illuminants,  297 

electrical  deposition  of,  300 

extraction  of,  299 

-extractors,  298,  300  . 

for  heating  retort  settings,  96 

in  crude  gas,  333 

means  of  taking  off  from  hydraulic,  170 

mechanical  removal  of,  296 

nitrogen  in,  258 

properties  of  modern,  269,  277 

quantity  obtained  per  ton  of  coal,  277 

-shield  for  hydraulic  main,  164 

-spray,  293,  299 

-towers,  74,  172,  330 

water  gas,  496 
Telphers,  209,  213,  217 

speed  and  capacity  of,  222 
Temperature  attained  in  test  furnaces,  135 

combustion  chamber,  49,  98,  140 

drop  in  condensers,  297 

in  vertical  retorts,  118 

of  carbonization,  254,  255,  274,  282 

of  producer,  49 

of  retort,  49,  140,  282 

of  waste  gases,  50,  97 

of  water-gas  apparatus,  485,  492 

secondary  air,  50 

throughout  coal  charge,  281 
Temporary  stops,  89 
Tests  for  cyanide  in  coal  gas,  381 
Thermal  balance  of  retort  setting,  93,  94 
of  water  gas  plant,  499 

losses  in  a  retort  setting,  94,  96,  97,  154 
"  Thermalite  "  insulating  brick,  140,  154 
Thiophen  in  coal  gas,  261 
Ties,  stresses  in  gasholder,  439 
Titanic  oxide  in  fireclays,  133,  134 
Toluene  in  coal  gas,  264,  302,  303 
Towers,  tar,  172 
Travelling -tray  conveyor,  209 
Tunnel  for  coal  store,  250 
Turbo-exhausters,  322 

fans,  483,  488 
Tysoe,  J.,  92 

Unaccounted-for  gas,  9 
Units,  capacity  of  various,  12 
Unoxidized  hydrogen  in  coal,  237,  256 
Unsaturated  hydrocarbons,  263 
Urea,  formation  of,  380 

Vacuum,  on  hydraulic  main,  90,  167,  275,  306 

regulation  of,  178 
Valency  of  the  elements,  263 
Valves,  centre,  for  purifiers,  410,  413 

cost  of,  413 

rack  and  pinion,   411,   413 


Valves,  reversible  for  purifiers,  395 

tier  valves  for  purifiers,  405 

water  type,  412 

Week's,  413 

weir-,     164,  171 
Vapour  pressure,  296 
Ventilation  of  retort  house,  41 
Vertical  condenser,   288 
Vertical  Retorts,  100 

advantages  of,  101,  102 

auxiliary  gas  take-off  for,  118 

capacity  of,  12,  72,  101,  128 

per  unit  of  ground  area,  72,  128 

capital  expenditure  on,  128 

coke  extractors  for,  103,  108,  117,  128 

coke  used  as  fuel  with,  47 

composition  of  gas  from,  284,  285 

cost  of  carbonization  with,   102,  128 

Dessau  type,  99,  100,  108,  129 

disadvantages  of,  102 

Elland  type,  101,  111 

flame  development  in,  99 

foundations  for,  33 

Glover-West  type,  12,  98,  99,  100,   103, 
128 

grate  area  for,  105,  108,  111,  116..  128 

ground  area  required  for,  101,  128 

Herring's  type,  101,  116,  129 

Holmes-Winstonley  type,  10],  US 

horse  power  required,   107,   108 

houses  for,  35,  38,  4],  128 

labour  charges  with,  102, 128 

method  of  heating,  128 

of  heating  air  supply,  66,  98 
of  quenching  coke,  128 

naphthalene  and,  279 

passage  of  gas  in,  283 

period  of  charge,  128> 

porous  charge  for,  111 

shape  of  retorts,  128 

speed  of  coal  through,  128 

size  of  retorts,  128 

temperatures  in  118,  282 

Wilson's  (Glasgow)  type,   101,  114,  128 

Woodall-Duckham  type,   12,  64,  98,  99. 

100,  102,  104,  128 
\rirgin  liquor  from  coal,  262,   328 
Volatile  matter  in  coal,  234,  235,   238 

in  coke,  279,  283 
Voluminometer  for  fireclays,  138 

Walker's  washer,  337 
Walls,   pier  and  buttress,  58 
Washers  for  coal,  243 
for  gas,  326,  333 

capacity  of,  354 

Cockeys,  335 

Dempster's,  335 

Livesey's,  334 


INDEX 


529 


Washers  for  gas,  mechanical,  339,  354 
"  Multiple,"  337 
Walker's,  337 

for  naphthalene,  342,  344,  396 
Washer-scrubbers,  339 

capacity  and  size  of,  15,  22,  346,  354 

centrifugal,  343 

"Eclipse,"  342 

Holmes',  342 

horse-power  required  for,  346 

"  Standard,"  340 

types  of,  340 

washing  bundles  for,  341 

Whessoe,    341 
Waste  gases,  composition  of,   49 

loss  of  heat  through,  94 

regulation  of,  68,  84,  88 

temperature  of,  50,  97 
Water,  admission  to  ascension  pipes,  160 
to  washers,  339,  356 
to  washer-scrubbers,  356 

admixture   with   coals,    160 

level,  7,  31,  41,  42 

obtained  from  coal,  262 

of  combination  in  oxide  of  iron,  384 

required  for  wet  purification,  333,  356 

supply,  8 
Water  Gas,  466 

admitted  to  hydraulic  main,  181 

advantages  compared  with  coal  gas,  466 

air  meters  for,  489 

air  required  for  "  blow  "  489 

Bsckton  plant,  475 

"  blow  "  products,  481 

"  Brighton  "  oil  spray,  493 

carbon  monoxide  in,  468,  470,  486 

carburation  of,  491 

clinkering,  490 

coke  used  for  making,  493 

composition  of,  495,  498 

cost  of,  494 

cost  of  plant,  25 

Dellwik  plant,  481 

"  Double-Gas  "  plant.  502 

effect  on  naphthalene  in  gas,  304,  467 

enriching-oil  for,  498 


Water  Gas,  fans  for,  483,  488 

ground  area  required  for  plant,  466 

Humphreys  and  Glasgow  plant,  470 

industrial  uses  of,  506 

"  K  and  A  "  plant,  478 

Merrifield-Westcott-Pearson  plant,  476 

methane-hydrogen  plant,  501 

neat-oxygen  method,  469 

oil  used  for  carburetting,  4915 

period  of  "run  "  and  "blow,"  490 

practical  considerations  affecting.  485 

pressure  of  blast,  488 

single  superheater  plant,  475 

size  of  purifiers  for,  16,  25 

specific  gravity  of,  7 

steam    generation    for,    507 

steam  meters  for,  487 

sulphuretted  hydrogen  in,  495 

tar,  496 

tar.  as  naphthalene  solvent   301,  302 

temperatures,  485,  492 

theory  of  manufacture,  468 

thermal  efficiency  of  plant,  499 

various  systems,  469 
Weathering   of  coal,   244 

of  fireclays,  132 
Weir  valve,  164,  171 
Weldon  mud,  384,  386 
West's  stoking  machinery,  184 
Wet   purification,    326    (see   Purification   also 

Washers,  Scrubbers) 
Wheeler  and  Burgess,  271 
Whessoe  washer-scrubber,  341 
Wilton's  cyanide  process,  370,  371 
Wind  pressure  on  gasholders,  428 
Winsor,  1 

Winstanley's    regenerator,    71 
Works    (see   under   Gasworks) 
Woodall-Duckham  vertical  retorts.  12,  64,  98, 
100,   102,  104,  128,  281,  283 

Xylene  in  coal  gas,  297 

Yield  per  ton  (see  "  Make  per  ton  ") 

Zimmer  on  conveyors,    200,    207 


Butler   &  Tanner   Frome  and  London 


M  M 


INDEX  TO    ADVERTISERS 


PAGE- 
ALDER  &  MACKAY   .          .          .  .  -.  .  .  .  •  ...  •  ,\  .    xliii 

ALDRIDGE  &  RANKEN       .          .  .  .  .  •-..'.  .  .        li 

ALLAN,  JOHN  &  Co.         .          .  .  .  .  .  ' .  .  . .  •    „     Ixv 

ALLAN,  THOS-.,  &  SONS,  LTD.    .  .  .  .  .  .  .  '•'•,  .      lix. 

ASHMORE  BENSON,  PEASE  &  Co.,  LTD.  .  .  .  .  .  .  ».  '     xl 

AVERY,  W.  &  T.,  LTD.    .          .  .  ',  .  .  .  .  '      ,  .  Ixviiii 

BABCOCK  &  WILCOX,  LTD.         .  '.  .  '  .  .  .  .  ...'"  •••-,...,  Iviii 

BLAND  LIGHT  SYNDICATE,  LTD.  .  .  .  .  .  •• . ~   .      .    xlvi 

BOURNE,  C.               .          .         .  ...  .  .  .  .  ,       Iv 

BRITISH  THOMSON-HOUSTON  Co.,  LTD.  .  .  .  .  .  ,  ..      xli 

CANNON  IRON  FOUNDRIES,  LTD.  -.  .  .  .  .  .  ,  .  xxxi 

CAPTIVE  FIRE  Co.,  LTD.  .       ,  .  .  .  .  .  .  .  .xxxiii 

CHEMICAL  ENGINEERING  Co.  ,  .  .  .  .  .  ^  .       iv 

CLAPHAM  BROS.,  LTD.       .         v  ..  •  •  •  .  .  -  -  •  xxiii 

CLAYTON,  SON  &  Co.,  LTD.       .  .  .  .  .  .  .  xlviii 

COCKEY,  E.,  &  SONS,  LTD.      *.  .  .";  .  .  .  .  -  ~   Ixiii 

COWAN,  W.  &  B.     .          .          .  .  .  .  .  .  .  ,  "'.'.  xiii 

CROSSLEY  BROS.,  LTD.      .      .„ :-  .  .  .  .  .  .  .  •-     Ivii 

CUTLER,  S.,  &  SONS,  LTD.       '.  ."  .  .  .  .  .  .  xi 

DAVIS  BROS.             .               ! ';.  .  .  .  .  .  .  .    Ixvi 

DEMPSTER,  R.  &  J.,  LTD.       -.  ..  /  .....  .         x 

DONKIN  COMPANY,  LTD.  (THE  BRYAN)  :  "  .  .  .  .  ...    xlv 

DRAKES,  LTD.  .    xlix 


FLETCHER,  RUSSELL  &  Co.,  LTD. 

GIBBONS,  B.,  JUN.,  LTD.  . 

GIBBONS  BROTHERS,  LTD.          .         V 

GLOVER,  THOS.,  &  Co.,  LTD.     .          . 

HATTERSLEY  &  DAVIDSON,  LTD.        . 

HAUGHTON'S  PATENT  METALLIC  PACKING  Co.,  LTD. 

HIRD,  CHAMBERS  &  HAMMOND. 

HOLMES,  W.  C.,  &  Co.,  LTD.    .... 

HUMPHREYS  &  GLASGOW,  LTD. 


Ivi 

.  xxxiv 
.  xxxv 
.  xxvii 

lii 
Ixii 

.  xxxvi 
xxxvii 

xxi 


ii  INDEX   TO   ADVERTISERS 

PAGE 

INDENTED  BAR  &  CONCRETE  ENGINEERING  Co.,  LTD.         ....    xlvii 

JENKINS,  W.  J.,  &  Co.,  LTD xlii 

K.  &  A.  WATER  GAS  Co.,  LTD.         .......          .xxviii 

KlRKHAM,   HULETT   &    CHANDLER,    LTD.         .  .  .  .  .  .  .          vii 

LE  BAS,  EDWABD  &  Co. ix 

LEE,  HOWL  &  Co.,  LTD.           .........     Ixiv 

LEEDS  &  BRADFORD  BOILER  Co.,  LTD.      .......       lix 

MACPHERSON  (DONALD)  &  Co.,  LTD..         .......     xxx 

MAIN,  R.  &  A.,  LTD.       .          .          .          .          .          .          ...          .  xxvii 

MARSH,  T.  G \.         .          .  xxix 

MELDRUMS,  LTD.      .          .          .         .         .          .          ....          .      liv 

NATIONAL  STEAM  CAR  Co,,  LTD.       '.          .          .          .          .         „         .  Ixi 

NEWTON,  CHAMBERS  &  Co.,  LTD.      ........       xii 

PARKINSON,  W.,  &  Co .  .xxxix 

PEARSON,  E.  J.  &  J.,  LTD.       .         .         .          .         .          .  .       iii 

PIGGOTT,  THOS.,  &  Co.,  LTD ,  .  .         1 

PORTER  &  Co.          .         .         .         .  .         .  '  '.  .  .     xiv 

POTTERTON,    THOS.     .  .  .  .  .  .  .     '         .  .  .  XXXviii 

REAVELL  &  Co.,  LTD.       .         .          .         .         .          .         ..         .         .         .      xvi 

RUSSELL,  JOHN,  &  Co.,  LTD.    .         .         ....  /  .  xxxii 

RUSTON,  PROCTOR  &  Co.,  LTD.          .         .         .         .         ...         .     xxv 

SCOTTISH  TUBE  Co.,  LTD.          .         .  .  .  ...  .  .        v 

STEWARTS  &  LLOYDS,  LTD.       .         .  .  .  .        ...         .  .  .     xix 

STRACHAN  &  HENSHAW,  LTD.            .  .  .  ...  .  xv 

STURTEVANT  ENGINEERING  Co.,  LTD.  .  .  ...  .  .    Ixvii 

TAYLOR,  J.,  &  Co .         .         .         .         .       vi 

TORBAY  PAINT  Co.  .          .         .          .          .         .          ...          .          .xxviii 

VALE,  THOS.,  &  SONS,  LTD.      .         . Ix 

VERTICAL  GAS  RETORT  SYNDICATE,  LTD.  .         .         .         .         .         .         .     xxii 

WALKER,  C.  &  W.,  LTD.           .          .          .......  xxiv 

WALLER,  GEORGE,  &  SON          .........  viii 

WATTS,  E.  R.,  &  Co xviii 

WEST'S  GAS  IMPROVEMENT  Co.,  LTD.         .......  xxvi 

WILLIAMSON  CLIFF,  LTD.           .         .         .         .         .         .         .         .         .  xx 

WlNSTANLEY   &    Co..  .  .  .  .  .  .  .,",...  .  .        liii 

WOODALL-DUCKHAM   Co.,    LTD..  .  .  .  .  .  .  .  .      xvii 

WRIGHT,  ALEXANDER,  &  Co.,  LTD.  .  .    xliv 


MODERN  GASWORKS  PRACTICE  iii 


E.  J.  &  J. 
PEARSON, 


LIMITED. 

STOURBRIDGE. 


of    II  i^li-Gr-^elo    R.oioi-ls» 


Contractors 

f  O»"        I  llO 

ERECTION 

of  Retoi*i  Settings  o£ 
description. 


•• 


44  A"  Qualilv  Retorts  and 

fii-ohi-icks,    Generator    & 

Regenerator  Settings 

for    small     Woi-ks. 


N.K.     Exceptional  results 
HAVE       BEEN      obtained. 

References  and    Figures 
upon      Application..     .*.     .*. 


Telegrams  :     "  Firebrick,'5   Stourbridge. 
Telephone  :     No.  9,  Brierley  Mill. 


IV 


MODERN   GASWORKS   PRACTICE 


WILTON'S 

Process  for  the  Recovery 


of 


BENZOL  AND  TOLUOL 


PLANT  IN  OPERATION  AT  ETRURIA  GASWORKS.        Harold  E.  Copp,  Esq.,  Engineer. 

OVER     20     PLANTS      IN     OPERATION 
AND    UNDER    CONSTRUCTION. 

For  full  particulars  write 

THE  CHEMICAL   ENGINEERING  CO., 

HENDON,    LONDON,    N.W. 


MODERN  GASWORKS  PRACTICE 


THE 

SCOTTISH  TUBE  CO. 

LIMITED. 

Telegrams:  "  Scotubeco,  Glasgow."        Telephone:  5687  Central  (6  lines). 

STEEL  PIPES 

With  Welded  Joints  to  Make  Continuous  Mains 

for 

HIGH-PRESSURE    GAS     DISTRIBUTION. 

Dipped  in  Dr.  Angus  Smith's  Solution.     Wrapped  with  Hessian  Cloth  and  Re-Dipped 


Wroupht-lron  &  Steel  Tubes  &  Fittings  for  Gas,  Water  &  Steam 

HEAD  OFFICE  :    34  Robertson  Street,  GLASGOW. 

Branches  :  London,  Manchester,  Cardiff,  Newcastle-on-Tyne,  and  Liverpool. 

Works  :   Coatbridge,  Rutherglen,  Glasgow,  and  Garnkirk. 


VI 


MODERN    GASWORKS     PRACTICE 


SULPHATE  OF  AMMONIA 
SATURATORS 


OVER  545  SATURATORS  DELIVERED  DURING  THE  LAST  FEW  YEARS- 


Chemical  Plant  Engineers, 

JOSEPH  TAYLOR  &  Co.,  BLAC*H°RSE  ST 

BOLTON. 


Telegraphic  Address          . 
SATURATORS,   BOLTON." 


Works  Telephone  No. 
848  BOLTON. 


Residence 
119   BOLTON. 


MODERN   GASWORKS   PRACTICE 


Vll 


PATENT  "STANDARD" 
CENTRIFUGAL   WASHERS 

For  Extraction  of  Ammonia,  Toluol,  Cyanide,  Benzol, 
::     Naphthalene,    etc.,  from   Coal  and  other  Gases.     :: 


Patent    ''Standard"   Centrifugal   Washers    (and    "  Standard"  Tar  Washers)  at  the  Southa  11 
Station  of  the  Brentford  Gas  Company. 


Total  Daily  Capacity  of 
machines  ordered  : 


143, 07O,OOO  cubic  feet. 


KlRKHAM,  HULETT  &  CHANDLER,  LTD., 

132  &  133  PALACE  CHAMBERS,  BRIDGE  STREET,  WESTMINSTER,  S.W. 

Telegraphic  Address:  "WASHER,  LONDON."  Telephone  No.  127  VICTORIA. 


Vlll 


Exhausting   Machinery 

OF,  ALL    CAPACITIES    AND    FOR   ALL    PURPOSES. 
WALLER'S  THREE  AND  FOUR  BLADE  EXHAUSTERS. 


HIGH   PRESSURE   GAS  PLANTS. 

RECIPROCATING     COMPRESSORS. 
ROTARY    COMPRESSORS. 
BOOSTING  FANS,    etc. 

STEAM,     GAS,     OR     ELECTRICALLY    DRIVEN. 
—  DISTRICT     OR     SERVICE     GOVERNORS. 


PUMPS  FOB  TAwATLErB  OB  PUMPS 

Coke  Breaking,  Screening  and  Elevating  Plants 

GAS   VALVES 

OF    ALL     SIZES. 
HYDRAULIC     LIFTS     AND     TRUCK    TIPPERS. 


LIVESEY    AND     ROTARY    WASHERS. 


"  REESON  "  PATENT  RETORT  HOUSE  GOVERNORS 


"  UNDER -PRESSURE  "     DRILLING    APPARATUS. 


GEO.   WALLER  &  SON, 

PHffiNIX    IRON    WORKS, 
STROUD,  GLOUCESTERSHIRE. 

Telegrams:  Waller,  Brimscombe.  Telephone:  No.   10  Brimscombe. 

Agents  for  Scotland :    D.  M.  NELSON  &  CO.,  20  West  Campbell  St.,  Glasgow. 


MODERN   GASWORKS   PRACTICE 


IX 


FITTINGS 

HIGH  PRESSURE  PIPE  WORK^ 
COILS.&C 


USED  BY  GAS  AND  WATER  COMPANIES 

in  all  Countries.  7,000  varieties.  Send  for  Catalogue. 

Gmm 
r  J™  have  the  Largest  Sale  of  any  Fittings. 

SEND    US    YOUR    ORDERS,   t! 


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AS    LARGE    AS    WE    LIKE. 


The   Reliable 

PRATT  &CADY 

Iron  Body 
GATE  VALVES  for  GAS. 

Double  Disc.        Parallel  Seats. 

ALL  IRON.      10-in.  to  60-inch. 

With  Handhole  at  side. 

Simple,     Strong,     Durable. 

This  Valve  Never  Sticks. 

Specially  adapted  for  Gas  Installation. 


Sectional.  Outside  Screw 

EDWARD    LE    BAS    &    CO.,   E^STi 

Write  for  220-page  Complete  Catalogue  of   Valves  and  Cocks. 


Flanged. 

*** 


MODERN   GASWORKS   PRACTICE 


mm--,       . 

BEARSGOT 
SPECIALITIES 


Are 

up 

of 


synonymous  with 
.to-date  Gas  Apparatus 
every  description  from 


Retort  House 
to  Gasholder. 

For  particulars  apply  to 

DEMPSTER 
MANCHESTER. 


Telegrams  : 
••  Scrubber 
Manchester. 


MODERN   GASWORKS   PRACTICE  xi 

SAML  CUTLER  &  SONS,  LTD. 

PROVIDENCE  IRONWORKS,  39  VICTORIA  STREET, 

MILLWALL.  WESTMINSTER. 

LONDON. 

GASHOLDERS. 

CONDENSERS.    WASHERS.    SCRUBBERS. 

PURIFIERS. 

CARBURETTED  WATER  GAS  PLANTS. 

COAL  AND  COKE  HANDLING  INSTALLATIONS. 

BLUE  WATER  GAS  PLANTS. 

HYDROGEN  PLANTS. 

OIL  AND  WATER  TANKS. 

ELECTRIC  TELPHERS. 

EVERY    REQUIREMENT    FOR     GASWORKS 
FROM     RETORT    TO    GASHOLDER. 


No.  310. 


Xll 


MODERN   GASWORKS   PRACTICE 


Telegrams  :  "  NEWTON, 

SHEFFIELD. " 


ESTABLISHED  7793. 


Telephone : 
CENTRAL  2200 

Two  Lines. 


NEWTON,  CHAMBERS 

&  Co.,  Ltd., 

THORNCLIFFE   IRONWORKS  near  SHEFFIELD. 


GASHOLDERS: 

Standard  Guided  or  Spiral. 


SCRUBBERS. 


PURIFIERS. 


BRANCH     OFFICES 

LONDON  :   Brook  House, 

10-12  Wai  brook,  E.C. 

LIVERPOOL:  50a  Lord  Street,  W. 


MANCHESTER:  Grosvenor  Buildings, 
\  Deansgate. 

SHEFFIELD:   Moorhead. 


MODERN   GASWORKS   PRACTICE  xiii 

COWAN'S 

WET  METERS    DRY  METERS 


In  Tin  and   Cast-iron  Cases, 


In    Tin    Cases    and    in    Im- 


with  the  Warner  and  Cowan  ^               ^ 

r\                i   \v7-ir         n          »  I     proved  Cast- Iron  Cases,  with 

Drum,  and    William  Cowan  s  I 

Syphon  Overflow.  all  the   Latest    Improvements. 


STATION    METERS,   STATION   GOVERNORS, 
RETORT   HOUSE   GOVERNORS, 

Fitted  with  our  Patent  Form  of  Valve  which  ensures  Perfect  Regulation. 
TESTING   GASHOLDERS  AND    TEST  METERS. 

PRESSURE  AND  EXHAUST  REGISTERS,  PRESSURE  GAUGES,  Etc, 

SERVICE  CLEANSERS. 

METERS   FOR    LAMP    PILLARS,   FOOTWAY    METER    BOXES, 

AND  OTHER  GAS  APPARATUS. 


COIN-IN-THE-SLOT   METERS. 


W.  &  B.  COWAN 

INCORPORATED  IN  PARKINSON  and  W.  &  B.  COWAN,  Ltd. 
FITZALAN  STREET  WORKS,  KENNINGTON  ROAD,  LONDON,  S.E. 

Dalton  Street  Works,  Newtown,  MANCHESTER;  Buccleuch  Street  Works,   EDINBURGH  ; 

The  Glasgow  Meter  Works,  57  John  St.,  Bridgeton,  GLASGOW  ;   Hill  St.  Works,  BELFAST; 

Commonwealth  Meter  Works,  Macquarie  Place,  SYDNEY  ;  489  Flinders  Lane,  MELBOURNE; 

33  Turbot  Street,  BRISBANE  ;  Ballance  Street  Works,  WELLINGTON,  N.Z. 


THE  STANDARD  METER  COMPANY,  Ltd. 

(TORONTO,    Ont. ;    VANCOUVER,    B.C.) 


xiv  MODERN   GASWORKS   PRACTICE 

WE   SPECIALIZE 

IN 

SMALL   GAS-WORKS 

and 

SOLICIT  INQUIRIES  FOR  COMPLETE  WORKS 


or 


EXTENSIONS  AND  RENEWALS. 


Makers    of   Gasholders,    Purifiers,    Scrubbers, 
Condensers,  &c.,  &c. 


Cast  Iron  Columns,  Tanks,  and  Constructional  Works. 

Complete  Oxy-Acetylene  Welding  and  Cutting  Apparatus. 

Only  First-Class  Materials  and  Workmanship. 


PORTER    &   CO., 

Gas  Engineers,  LINCOLN,  ENG 

Established  1855.  Telegrams  :  "  PORTER,  LINCOLN."  Telephone  No.  266. 


MODERN   GASWORKS   PRACTICE 


XV 


OUR   SYSTEM    IS   EXTENSIVELY 

USED    FOR    HANDLING    HOT 
COKE    DIRECT   FROM   RETORTS. 


•S"IVOB±JJ3A    HXIM    NOLL03NNOO    NI 

TVOO   QNV  33IOO    HXO9   ONI1QNVH 

SXNVld    AMVW    MOHS    NVO    3AV 


XVI 


MODERN   GASWORKS   PRACTICE 


BELT 

DRIVEN 

SINGLE 

STAGE 

QUADRUPLEX 

COMPRESSOR 


"REAVELL"   COMPRESSORS. 

FOR    AIR    OR    GAS. 
REAVELL  &  CO.  Ltd.,  IPSWICH,  ENGLAND. 


BELT 

DRIVEN 

SINGLE 

STAGE 

DUPLEX 

COMPRESSOR 


MODERN  GASWORKS  PRACTICE  xvii 

The 

WOODALL-DUCKHAM 
SYSTEM 


of    continuous    carbonization 

ENSURES     .     . 

ECONOMY 


of 


and 

GROUND   SPACE. 


n    n     n     n 


For  particulars  apply  to 

WOODALL-  D  UCKHAM  •  C?  -I™ 

PALACE    CHAMBERS 

WESTMINSTER 

SW. 


xvui 


MODERN   GASWORKS   PRACTICE 


FACSIMILE  of  a  POSTCARD 
from    a    CONSUMER    of 
GAS  for  LIGHTING 


"METRO"  burners 

make  satisfied  users  of  gas  because 

they  are  economical,  efficient  and 

easily  maintained. 

This   is   why  — 

Every  "Metro"  burner  is  adjusted 

to   suit    the   gas-  with   which  it  is 

intended  to  be  used.     The  burner 

and  globe  may  be  fitted  or  removed 

for  cleaning  with   the  same  facility  as  an  electric  bulb.      All 

parts    are   made    to   standard  gauges.     There  are  no  screws. 


FOR  PRICE  LIST  AND  FURTHER  PARTICULARS  WRITE  TO 

E.  R.  WATTS  &  SON 

123  CAMBERWELL  RD.,  LONDON,  S.E. 


XIX 


STEEL  PIPES 


FOR  HIGH  PRESSURE  GAS 

With  STEWARTS'  PATENT  WELDED  LONGSLEEVE  JOINTS  for  welding  up 

into  long  continuous  lengths  in  or  alongside  the  trench.    Joints  can  be 

made  without  turning  the  pipes  round. 


LIGHT  LAP-WELDED  STEEL  PIPES  with  STEWARTS'  PATENT  INSERTED  AND 
LONGSLEEVE  JOINTS  for  LEAD  AND  YARN. 

Suitable  for   Gas,    Water,   Air,   Sewage,   etc. 


Screwed  and  Socketed  Tubes.      Main  Steam.  Pipe  Installations. 


TO. 


STEWARTS'"  LLOYDS,  L 

41  Oswald  St.,  Glasgow — Broad  St.  Chambers,  Birmingham, 
Winchester  House,  London,  E.G. 


XX 


RETORTS 

All  Types  made  in  Fireclay  or  Silica. 

Large  makers   of  Segmentals  to   the   most   skilled 
buyers. 

Firebricks,  Blocks,  Ground  Fireclay  and  Silica. 
Refractory  Paints,  Glazes  and  Cements. 

Makers  of  all  classes   of  Fire-resisting  Products 
from  special  or  rare  minerals. 

THE  BEST  SERVICE 

is  at  your  command.  We  advise  on  Bricks  and 
Blocks  for  any  required  situation,  and  how  best 
to  cope  with  Gas,  Blast,  Slag  and  Chemical 
Action  in  all  classes  of  Gas,  Metallurgical  or 
Chemical  Furnaces. 


WILLIAMSON  CLIFF,  LD. 

Gas  Retort,  Fire  &  Silica  Brick  Works, 

STAMFORD,    ENGLAND. 

Telegrams:   "WILLIAMSON  CLIFF,   STAMFORD." 
'Phones:  WORKS  OFFICE,   16  STAMFORD;  other  Lines,  49  and  330  STAMFORD. 

LONDON  OFFICE:    17  MONUMENT  STREET,  E.G.    'Phone :  AVENUE  1771. 


MODERN   GASWORKS   PRACTICE  xxi 

HUMPHREYS  &  GLASGOW,  LTD. 

AND 

The  United  Gas  Improvement  Co.,  U.S.A. 

CARBURETTED  WATER  GAS 

NINE  REASONS  : 

1.  LOW  CAPITAL  COST. 

\ 

2.  Small  Ground  Space. 

3.  Control  of  Coke   Market. 

4.  Independence  of  Coal  and  Labour. 

5.  Calorific  and  Illuminating  Control.    . 

6.  Small  Sulphur  Content. 

7.  Freedom  from   Naphthalene. 

8<     Instant  Production  instead  of  Expensive  Storage. 
9.    CHEAPER  AND   BETTER  GAS. 

AND  THE  RESULTS 

Humphreys  and  Glasgow,  Ltd.    .  .    352,800,000  Cubic  Feet  Daily. 
The  U.G.I.CO.,  U.S.A 750,900,000  Cubic  Feet  Daily. 

OVER  ONE  THOUSAND  MILLIONS  CUB.  FT.  OAILV. 

BLUE  WATER  GAS 

38,  VICTORIA  STREET,  LONDON,  S.W. 


xxu 


MODERN    GASWORKS    PRACTICE 


INTERMITTENT  VERTICAL  RETORTS 


FOUL    MAIN 


DISCHARGING 
GEAR 


CROSS  SECTION  THROUGH  BED. 

THE  VERTICAL  GAS  RETORT  SYNDICATE  LTD.,  17  VICTORIA  ST.,  WESTMINSTER,  s.\v 


MODERN   GASWORKS   PRACTICE 


xxm 


xxiv  MODERN     GASWORKS     PRACTICE 


I  MI  MI  MI  MI  HI  HI  ii  MI  in  ii 


GASHOLDERS 


Milbourne  Patent  Roller  Carriages. 
Automatic  Lubrication. 


PURIFIERS   | 

Milbourne  Patent  Duplex  Valves,  Automatic  Cover  Q3 
Fasteners,  Safety  Discharge  Shoots,  Rubber  Jointing,  ^ 
"  Milbel "  Patent  Purifier  Grids.  rm 


MILBOURNE  PATENT 
REVERSE  FLOW  VALVES. 


MI 


STRUCTURAL  STEEL  WORK,  CONDENSERS, 
SCRUBBERS,  SULPHATE  OF  AMMONIA,  PURE 
CONCENTRATED  AMMONIA,  BENZOLE,  and  every 
description  of  GAS  AND  CHEMICAL  WORKS  PLANT 


|  C.  &  W.  WALKER, 

[M] 

ED          DONNINGTON,     NEWPORT— SALOP. 

nn 


MODERN   GASWORKS   PRACTICE 


RUSTON  EXCAVATORS 

ARE    IDEAL   TOOLS 

FOR  THE  ECONOMICAL  HANDLING  OF 

STOCK     PILES     OF     COAL     AND     COKE, 

AND    FOR    DEALING    WITH    WASTE    HEAPS. 


ELLE-CRUEaVAPEUR 
RUSTON 


Sole  Maker*  : 


RUSTON, 

PROCTOR     &    C°-     LTD 

LINCOLN,    ENGLAND. 

Telegrams:    "RUSTON,  LINCOLN."  Tel.:  580  LINCOLN. 

ESTABLISHED  1840.  WORKS  COMPRISE  100  ACRES.  5,400  EMPLOYEES. 


Also  Manufacturers  of 


BOILERS. 

Lancashire. 
Cornish. 
Flue  and  Tube. 
Loco-Multitubu- 
lar. 
Vertical. 

STEAM 
ENGINES. 
Simple   and 
Compound 
Fixed. 

INTERNAL  COMBUSTION  ENGINES. 

GAS 
PRODUCERS. 

For     Generating 
Gas  from  coal 
or  wood. 

PUMPS. 
Centrifugal  and 
Multi-stage. 

OIL. 

High   Efficiency    Crude 
Oil  Engines. 
Also  Refined  and  Crude 
Fixed,    Portable  and 
Loco  Engines. 

GAS. 
Fixed          Gas 
Engines    for 
TOAHS     and 
Producer  Gas. 

ALL  TYPES  AND  SIZES  OF  STEEL  TANKS,  STILLS,  ETC. 


XXVI 


MODERN   GASWORKS   PRACTICE 


GLOVER=WEST 

VERTICAL  RETORTS 


COAL    CONVEYOR 


COAL    BUNKERS 


COAL   VALVES 


COAL- FEED 
HOPPERS 


COLLECTING  MAIN 


FOUL    MAIN 

WASTE -GAS 

CIRCULATING 

CHAMBERS 

COMBUSTION 
CHAMBERS 


SECONDARY -AIR 
CHAMBERS 


COKE    EXTRACTORS 


DRIVING -GEAR  FOR 
COKE    EXTRACTORS 


COKE   CHAMBERS 


CHIMNEY 


Transverse  Section  of  Retort  House. 

WEST'S  GAS  IMPROVEMENT  CO.  LTD, 

ENGINEERS, 

MILES   PLATTING,   MANCHESTER. 


MODERN   GASWORKS   PRACTICE 


XXVll 


CONVINCING  TESTIMONY 


to  the 

efficiency 
of  the 

Thomas 

Glover 

Dry 

Meter. 


This  meter  was  fixed  in  Boston  Church  in  the 

year  1859.    It  is  still  there,  and  has  registered  to 

the  satisfaction  of  all  concerned  during  the  period 

of  57  years. 

THOMAS  GLOVER  &  Co.,  Ltd. 


(ORIGINAL     MAKERS,     ESTABLISHED  1844) 

GOTHIC  WORKS,  ANGEL  ROAD,   EDMONTON,  LONDON,  N. 

MANCHESTER       FALKIRK  GLASGOW 

BELFAST  MELBOURNE      SYDNEY. 


8  D  A  wr'Uirc  •     BIRMINGHAM 
B  RANCHES  .     BRISTOL 


MAINS 


Reliable 
Efficient 
Jiygienie 


R.  &  A.  MAIN,    LIMITED, 


WORKS:  Gothic  Works,    EDMONTON,  N.  ;    Gothic  Ironworks,  FALKIRK; 
and    Gothic   Works,    BIRMINGHAM. 


xxviii  MODERN   GASWORKS   PRACTICE 


THE   MOST   RELIABLE   PAINT 

FOR     GASWORKS. 

"The  moving  finger  writes" 

TORBAY    PAINT 

[REGISTERED  TRADE  MARK] 

"and  having  writ,  moves  on." 

O.K: 


THE  TORBAY  26,  27  &  28  Billiter  Street,  LONDON,  E.G. 

PAINT  CO.  39-41  Old  Hal1  Street-  LIVERPOOL. 


K.  &  A. 

BLUE  OR  CARBURETTED 

WATER  GAS. 

THE 

TWIN   GENERATOR   PLANT. 

(Blown  in   Parallel — Run  in  Series.) 


ESTIMATES  FREE. 


THE  K.  &  A.  WATER-GAS  CO.,  LTD,, 

56  VICTORIA    STREET,  WESTMINSTER,  S.W. 


MODERN     GASWORKS     PRACTICE 


XXIX 


xxx  MODERN  GASWORKS  PRACTICE 

WHY  TAMAC  FIRE  CEMENT 
FOR  GASWORKS? 


The  importance  of  using  "  Tamac  "  for  building  or  repairing  Retort  Settings,  includ- 
ing Retorts,  Furnaces,  Combustion  Chambers,  Flues,  etc. .cannot  be  over-estimated. 

The  life  of  a  Retort  Bench  depends  on  the  quality  of  the  Firebricks,  Retorts,  and  ALSO 
the  quality  of  the  material  that  is  used  for  fixing  them  together. 

The  strength  and  adhesive  properties  of  "  Tamac  "  at  high  temperature  and  under 
heavy  load,  is  one  of  the  important  reasons  why  "  Tamac  "  is  so  universally  used. 

Furthermore,  Fire  Clay  will  contract  in  use  under  high  temperature,  thus  tending  to 
make  the  structure  leaky,  but  "  Tamac  "  slightly  expands  on  heating,  thus  tending 
to  make  the  structure  tighter. 

Another  important  feature  in  "  Tamac  "  is  the  property  of  fluxing  at  moderate  tem- 
perature, this  is  the  gripping  power  which  gives  permanence,  in  other  words 
"  it  stays  put." 

Lastly  "  Tamac  "  represents  the  latest  phase  of  Laboratory  investigation,  combined 
with  practical  and  severe  tests.  The  raw  materials  are  scientifically  tested  from 
time  to  time,  and  the  manufacture  is  unvaryingly  uniform. 

That  is  why  "  Tamac  "  is  THE  material  without  an  equal  for  the  building  and  mainten- 
ance of  Retort  Settings,  the  working  conditions  of  which  were  never  more 
severe. 

Therefore,  when  contemplating  new  Retort  Benches,  SPECIFY  "  TAMAC  "  and  see 
that'  you  get  it,  as  that  will  ensure  perfect  work  for  the  least  outlay. 


The  Inventors  and  Sole  Manufacturers  of  Tamac  Fire  Cements  are  : — 

DONALD  MACPHERSON  &  Co,  Ltd. 

KNOTT  MILL, 

MANCHESTER. 

Tel.  Add.:  Foochow,  Manchester.  Tel.  897  Central. 


MODERN   GASWORKS   PRACTICE 


XXXI 


"GANNON"  GAS  GOODS 


ALWAYS 

ON 

THE 

SPOT 


MANUFACTURERS:— CANNON  IRON  FOUNDRIES  LTD.,  DEEPFIELDS,  NR.  BILSTON,  STAFFS, 
AND  BATH  HOUSE,  57-60  HOLBORN  VIADUCT,  LONDON,  E.G. 


XXX11 


MODERN   GASWORKS   PRACTICE 


JOHN  RUSSELL  &  Co.,  LTD.,  ^ 

ALMA     TUBE     WORKS,     WALSALL. 


—  and  Fittings  of  every  description.   — 
FOR     GAS,     STEAM,     WATER, 


GENERAL  ENGINEERING  F»URI>OSES. 


HIGH-PRESSURE    TUBES,    COILS    AND     SUPERHEATERS 

FOR      STEAM.     WATER      AND      ELECTRIC      POWER      INSTALLATIONS 


ACETYLENE- 

t  WELDING 
A 
PECIALITY. 
London  Office :  145  QUEEN  VICTORIA  STREET,  E.G. 


MODERN   GASWORKS   PRACTICE 


xxxin 


'Captive  Fire 

A  New  System  of  Gas  Heating 
FOR    ALL     PURPOSES. 


Brass  Melting, Steel  Heating, etc 

No  Expert  Adjustment  required 
to  right  any  wrong  principles. 


What  is  a  Pressure  Balance  ? 

A  device  which  ensures  a  constant  ratio  in  the  pres- 
sures of  air  and  gas,  and  which  ensures  an  unalterable 
mixture  whatever  the  variation  of  supply  pressures 
and  consumption  may  be. 

What  is  a  'Captive  Fire'  Furnace? 

A  furnace  device  heated  wtih  an  invariable  mixture  of 
gas  and  air  downwardly  displacing  the  flues  between 
an  inner  and  outer  jacket.  It  produces  a  perfect  and 
flameless  combustion,  and  its  efficiency  is  over  100 
per  cent,  better  than  any  hitherto  known. 


Correspondence  is  Cordially  Invited. 


THIS    IS   THE   CONTINUOUS   STEEL   BILLET 

HEATING   FURNACE.      MANY  OTHER  TYPES 

ARE   MADZ. 


'THE  CAPTIVE  FIRE 'GO,,  Ltd. 

34  Porchester  Terrace,  London,  W. 


xxxiv  MODERN    GASWORKS     PRACTICE 

B.  GIBBONS,  Junr.,  Ltd. 

DUDLEY. 

RETORTS 

(MACHINE-MADE). 

FIRECLAY   AND    SILICA 
BRICKS,  BLOCKS  AND  TILES. 


RESULTS    OF 

REFRACTORY   AND 
CONTRACTION     TESTS 

ON     THE     ACTUAL     MATERIAL     SUPPLIED,     AS 

MADE      IN      OUR       OWN      LABORATORY,      WILL 

BE    SUBMITTED    IF    DESIRED. 


HIGHEST  QUALITY 
ONLY    SUPPLIED. 

LONDON,  MANCHESTER,  MELBOURNE  AND  CARDIFF, 


XXXV 


THE 

GUEST-GIBBONS 
CHARGING   AND   DISCHARGING 

MACHINE 


For    the    VERY    BEST    in    RETORT 
HOUSE   DESIGN   and    EQUIPMENT 

Send  your  inquiries  to  : — 

GIBBONS   BROS.,  Ltd. 

DUDLEY. 

LONDON,     MANCHESTER,     MELBOURNE    &    CARDIFF. 


xxxvi  MODERN   GASWORKS   PRACTICE 


CONTINUOUS 


(HIRD'S    PATENT    SYSTEM) 

GAS  or  COKE  BREEZE  FIRED 

FOR 

i.      TAR  DISTILLING 
;       AND    DEHYDRATING, 
OIL   DEBENZOLIZING, 


Advantages  : 

LOW    WORKING    COST 

SIMPLE    TO    OPERATE 

FIRING    TUBES     RENEWABLE 
AT    SMALL    COST 

NO    PRESSURE 

NO    FUMES    OR     SMOKE 


Sole  Makers  : 


W.  C.  HOLMES  &  Co.,  LTD. 

Works  and  Head          HUDDERSFIELD. 


Offices    . 


MODERN   GASWORKS   PRACTICE  xxxvii 


W.  C.  HOLMES  &  Co.,  LTD. 

WHITESTONE  IRONWORKS  AND 
TURNfeRIDGE    FOUNDRY, 

HUDDERSFIELD. 

Telephone  1573.  Telegrams:  "Holmes,  H  udders-field." 


T-T      VALVES 
•*••*•       CONDENSERS 

Q        TAR  EXTRACTORS 
ROTARY  WASHERS 
CENTRIFUGAL  WASHERS 
PURIFIERS 
GASHOLDERS 
TANKS 
SULPHATE  PLANTS 


S 


STEEL  WORK 
SPECIAL   CASTINGS 


Holmcs-Winstanlcy  Vertical  Retorts. 


xxxvm 


MODERN   GASWORKS   PRACTICE 


"VICTOR"  GAS  BOILERS 

Hot  Water  for  Domestic  and  Trade  purposes  is  produced  by  "  Victor" 

Gas  Boilers  most  successfully.     They  are  designed  for  convenience 

of  erection  in  battery  form  and  a   complete   range   of    boilers    is 

provided   in  order  to  meet  every  requirement. 


'G"  Series,  Nos.  72-73. 


RETURN  INLET  I 
THERMOSTAT-^ 


"D"  Series,  Nos.   18,   19,  20 


Nos.  9,  10,  and  n.    Complete  Apparatus.  Ncs.  51,  52,  and  53.    Complete  apparatus. 

Separate  boiler  and  cylinder.  Self-contained  boiler  and  cylinder. 

Special  designs  of  apparatus  for  any  requirement  submitted  upon  receipt  of  ^particulars. 


Engineer 


Ett..     THOMAS   POTTERTON, 

CAVENDISH     WORKS,     BALHAM,     LONDON,     S.W. 

Telegrams  :  "POTTERTON  BAL.,  LONDON."  Telephone  :  STREATHAMil869. 


MODERN    GASWORKS    PRACTICE 


XXXIX 


PARKINSON'S 


STATION     METERS 
AND      GOVERNORS 

SUITABLE   FOR   BOTH 

HIGH   AND   LOW  PRESSURES. 

Also  ORDINARY  and  PREPAYMENT  METERS, 

TEST  GASHOLDERS,  PRESSURE  REGISTERS, 
GAUGES,  etc. 


W.  PARKINSON  &  CO. 

(INCORPORATED  IN  PARKINSON  AND  W.  &  B.  COWAN,  LTD. 


Cottage  Lane,  City  Road, 
LONDON. 


Bell  Barn  Road, 
BIRMINGHAM. 


Telegrams:     "  Index,  London,"     "  Gasmeters,  Birmingham." 
Telephone  Nos. :     7570  City;   2245  Midland,  Birmingham. 


xl 


MODERN   GASWORKS   PRACTICE 


G 


ASHOLDERS 

AND  GAS  APPARATUS 


PURIFIERS  SCRUBBERS 

CONDENSERS  WASHERS 

SULPHATE   OF   AMMONIA   PLANTS 
BENZOL  AND   TOLUOL   PLANTS,   &c. 


FOUR-LIFT  GASHOLDER,  CAPACITY  TEN  MILLION  CUBIC  FEET. 

MADE      AND     ERECTED     FOR     MANCHESTER     CORPORATION 
J.    G.   NEWBIGGING,    ESQ.,    ENGINEER. 


ASHMORE,  BENSON,  PEASE   &  Co.,   LTD. 

STOCKTON-ON-TEES 

TELEGRAMS  : 

"GASHOLDER" 


MODERN     GASWORKS     PRACTICE  xli 


For  Gas  Retorts  and  Coke 
Ovens 

To  exhaust  the  gas  from  retorts  and  coke  ovens 
economically,  a  thoroughly  reliable  exhauster  capable 
of  continuous  operation  for  long  periods  without 
shutting  down,  is  required. 

TURBO    GAS    . 
EXHAUSTERS 

possess  the  above  advantages  in  a  marked  degree,  one 
machine  installed  recently  completing  a  six  months' 
run  without  once  shutting  down. 

These  exhausters  have  been  designed  by  British 
engineers,  and  are  built  by  British  workmen  in  Rugby, 
England. 

As  compared  with  reciprocating  engine  driven  ex- 
hausters, they  have  low  initial  and  maintenance  cost, 
are  of  small  size  in  comparison  to  output,  have  low 
steam  consumption,  and  large  internal  clearances, 
rendering  internal  lubrication  unnecessary. 

They  are  provided  with  an  extremely  sensitive  form 
of  governor,  which  ensures  the  maintenance  of  a 
perfectly  steady  vacuum  regardless  of.  variation  in 
output. 

THE  BRITISH  THOMSON-HOUSTON  Co.,  Ltd., 
ELECTRICAL  ENGINEERS  AND  MANUFACTURERS, 
Head  Office  and  Works:    Rugby,  England. 


xlii 


MODERN   GASWORKS   PRACTICE 


MODERN 
GASWORKS  MACHINERY 


D.B.   Patent  Hot  Coke   Con- 
veyors. 


<[  D.B.     Patent    Charging    and 
Discharging  Machines. 


<]j  Brookes      Patent     Automatic 
Air  Boxes. 


€J  Electric  Telpher  Plants. 


Coal      and     Coke     Handling 
Plants. 


*    Generating  Plants. 

<$><•> 
<[  Wagon  Tippers. 


JENKINS  D.B.    PATENT  COMPLETE  STOKER. 


(f  Constructional  Steel  Work  and 
General  Castings,  etc.,  etc. 


ILLUSTRATION  OF  COKE  HANDLING  PLANT  ERECTED  BY  US. 


W.  J.  JENKINS  &  CO.  LIMITED, 


London  Office : 
15  VICTORIA    STREET, 
WESTMINSTER. 


RETFORD 


NO"! — TQ  Telephone  :  44  Retford 

'  '  ^-s    •     '   O«         Telegrams:       "Jenkins 


Retford. 


MODERN   GASWORKS   PRACTICE 


xliii 


ALDER 


MASKAY 


ESTABLISHED    1850. 


MANUFACTURERS   OF 


Wet  and  Dry  Gas  Meters. 
Prepayment  Meters. 
Station  Meters. 
Underground  Meters. 
Test  and  Experimental  Meters. 
Demonstration  Meters. 


Test  Holders. 
Pressure  Gauges. 
Brass  Work  of  every  Description. 
Gas  Lanterns. 

Automatic  Lighting  &  Extinguishing 
Apparatus  for  Street  Lamps. 


PREPAYMENT   VALVE 

ACCESSIBLE    WITHOUT 

OPENING    METER. 


ATTACHMENT     READILY 
DETACHABLE. 


NO   SPRINGS. 


SILENT   ACTION. 


COIN   CLOSER. 


LARGEST   CASH    BOX 
IN   THE    TRADE. 


THE    LARGEST    STUFFING 

BOXES     OF     ANY     METER 

MADE,  AVOIDING  LEAKAGE 

OR    SMELL. 


FIVE     HUNDRED 

REFERENCES 
HOME    AND   ABROAD. 


MADE  FOR  PENNIES,  SHILLING,  OR  ANY  COIN. 


Descriptive  List  and  all  Particulars  on  application. 


New   Grange  Works, 
EDINBURGH. 

Tel.  Address  : 

it" ALDER,  EDINBURGH." 
Tel.  No.  1431  Central. 

Ventnor  Street  Works, 
BRADFORD. 

Tel.  Address  : 
"ALDER,  BRADFORD." 
Tel.  No.  1222. 


13  Victoria  St.,  Westminster, 
LONDON,  S.W. 

Tel.  Address  : 

"ALDERUGI,  LONDON." 

Tel.  No.  7643  Victoria. 


Central  House,  New  Street, 
BIRMINGHAM. 

Tel.  Address  : 
"ALDERUGI,    BIRMINGHAM.' 


Bridge  Street, 
SYDNEY, 

NEW   SOUTH    WALES. 

Cable   Address  : 
"PLAYER,  SYDNEY." 

Lower  Taranaki  Street, 
WELLINGTON, 
NEW  ZEALAND. 

Cable  Address  : 
'BUTCHER,  WELLINGTON." 


xliv 


EADY   &    CLARKE'S 


PATENT 


QUALITO  METER 


Draws  Crude  Gas  from  the  Foul  Main  against  the 
Exhauster   Pull, 


Condenses  it  ;   purifies  it ;   tests  it  for  quality  and  provides  a  means 

(the  handles  shown  on  the   right)  of  instantly  loading   or  unloading 

the  Retort  House  Governor  until  a  level  quality  is  obtained. 


ALEX.    WRIGHT  &    Co.,  Ltd., 

1   Westminster  Palace  Gardens, 

Victoria  Street,  Westminster. 


THE 


BRYAN  DONKIN  COMPANY  LTD 


OUR  SPECIALTIES.— 

GAS  EXHAUSTING  PLANTS 

In  capacities  from  100  to  750,000  c.f.p.  hour  to  suit  all  conditions. 

RATEAU  TURBO  EXHAUSTERS,  BLOWERS  &  FANS. 

Driven  by  Steam  Turbine,  Gas  Engine,  Electric  Motor  or  Belt ; 
for  Pressure  Raising,  Gas  Compressing,  dealing  with  gas  from 
Coke  Ovens,  etc. 

ROTARY  BLOWERS  &  COMPRESSORS 

Of  positive  type  for  Industrial  Purposes.  A  large  number  sup- 
plied for  us 3  in  connection  with  Gas  Furnaces,  etc. 

RECIPROCATING  GAS  COMPRESSORS  for  high  pressures. 
COMBINED  METER  BLOWERS  for  oxide  revivification. 

PATENT  DISTRICT  GAS  GOVERNORS. 

Capable  of  reducing  with  accuracy  any  pressure  up  to  50  Ibs. 
per  sq.  inch  down  to  the  ordinary  district  pressure  in  one  stage. 
Absolute  certainty  of  action  under  all  conditions. 

HIGH  &  LOW  PRESSURE  REGULATORS 

For  Gas  Services,  Meters,  Gas  Fires  and  Cookers.  (Thousands 
supplied.) 

GAS  VALVES 

of  all  sizes  and  types,  for  all  purposes.    Single  &  Double  faced. 

GLAND  PLUG  COCKS.        SERVICE  CLAMPS  &  FITTINGS. 
TAR,  LIQUOR  &  WATER  PUMPS. 


HIGH  PRESSURE  GAS  DISTRIBUTION  SCHEMES  QUOTED  FOR. 


All  our  machinery  is  of  the  very  highest  class 
and  can  be  inspected  under  test  before  delivery. 


Head  Office  and  Works  : — 

CHESTERFIELD,    England. 


xlvi 


MODERN  GASWORKS  PRACTICE 


THE 


"BLAND"  Patent  BURNER 


A  No.  6. 
Household  Burner. 


C  No.  7. 
For  Factory,  Mill,  Office,  etc. 


NEW  TYPE 
BLANLITE  OUTDOOR  LAMP 

British    Made  . 


No.  9981.     300  c.p.  Burner.  No.  15.  3-light. 

THE    BLAND     LIGHT    SYNDICATE,     LIMITED, 

63  QUEEN  VICTORIA  STREET,  LONDON,  E.G.    (4  doors  from  Mansion  House  Station). 
6  BARNFIELD,  URMSTON,  MANCHESTER. 


T  I  (  "  Blanlite,  Cannon,  London." 

telegrams  (  "  Blanlite<  Urmston<  Manchester." 


(  London  :  Central  5647  (3  lines). 


TIL          <  LMnaon  :  Central  304/   (1  I 
telephones    ,  Manchesler  .   (Jrmston  2!6 


MODERN    GASWORKS     PRACTICE 


xlvii 


Indented  Bar  and  Concrete  Engineering  Co.,  Ltd, 

Specialists  in  Reinforced  Concrete  Designs  for  Gasworks,  etc. 

COAL     HOPPERS,     GASHOLDER     TANKS,     BUILDINGS,     etc. 
QUEEN     ANNE'S     CHAMBERS,     WESTMINSTER,      S.W. 


This    Coal    Hopper  at  Thrislington  Colliery    is  entirely  of  reinforced  concrete.     It 

is  90  feet  high,  and  has  a  capacity  of  1,100  tons  in  eight  compartments. 

It  was  designed  by  us. 


xlviii 


MODERN     GASWORKS     PRACTICE 


CLAYTON,  SON  &  GO.  LTD 

LEEDS. 


GASHOLDERS     AND     TANKS 
OF    ANY    SIZE   AND  DESIGN. 


PURIFIERS.          STRUCTURAL     WORK.          TANKS. 
WELDED  AND  RIVETTED  STEEL  PIPES.     BOILERS 


Telegrams  :  "GAS,  LEEDS."  Telephones  :  543  and  3433. 

LONDON  OFFICE  :  60  Queen  Victoria  Street,  E.G. 


MODERN   GASWORKS   PRACTICE 


xlix 


COAL  AND  GOKE  HANDLING  PLANTS  A  SPECIALITY. 


ESSENTIAL 

TO 

MODERN  GASWORKS. 


SEND  US  YOUR  ENQUIRIES. 


\ 


\ 


T\     \    \     \    \     \     \ 


MODERN   GASWORKS   PRACTICE 


THOS.  PIGGOTT  &  CO. 

LTD. 

MANUFACTURERS     OF 

GAS     MAKING    PLANT,     CONDENSERS,     ETC. 
TANKS,     STILLS,     PIPES,     Welded    and    Rivetted. 

CHIMNEYS,     OIL     TANKS,     ETC. 

ENGINEERING    AND     CONSTRUCTIONAL     WORK     OF     EVERY 

DESCRIPTION. 

MAKERS    OF    HUMPHREY'S    and    GLASGOW    C.W.G.    PLANT. 


Three  Lift  Gasholder,  212  ft.  6  in.  dia.  x  120  ft.  deep. 
PIGGOTT'S     PATENT     PRESSED     STEEL     TANKS. 

LARGE  STOCKS  ALWAYS  ON  HAND. 

FEEDING    HOPPERS     AND    COAL     BUNKERS. 
IRON    CASTINGS     up  to  7  Tons  in  Weight. 


Atlas  Works,  Springhill, 

BIRMINGHAM. 


LONDON   OFFICE  : 
63    QUEEN   VICTORIA   ST.,   B.C. 


Telegrams  :  "Atlas,  Birmingham. 
Telephone  :  Central  3922  (3  lines). 


MODERN  GASWORKS  PRACTICE 


39  VICTORIA   STREET. 
LONDON,   S.W. 


Tele 


phone  :    5118  Victoria, 
grams  :     Motorpathy,  Vic. 
London. 


EGISTEREO 


Complete 

Coal  =  Handling 

Plants. 


REGISTERED 


With  all 
Accessories. 


ALDRIDGE 


TRADE        MAR 


AVONBANK      WORKS, 
BATH. 


Tele 


phone  :   536    Bath, 
grams  :  Simultane,  Bath. 


Hi 


MODERN   GASWORKS   PRACTICE 


HATTERSLEY  &  DAVIDSON,  L 


TD 


Telegrams: 

"GEARING, 
SHEFFIELD." 


SHEFFIELD. 


Phone : 
4684 

(3  lines). 


FOR     ALL     MANNER     OF 

GASWORKS    TOOLS    AND    APPLIANCES. 


MODERN     GASWORKS     PRACTICE 


liii 


fflr 


WOULD 


PER  TON  SATISFY  YOU  ? 


WE"  CAN  REFER  YOU  TO  OFFICIAL  FIGURES  IN  THE 

"GAS    WORLD"  ANALYSES   PROVING  WHAT  OUR 

SETTINGS    HAVE     DONE     OVER     AND     OVER     AGAIN 
WITH    SPLENDID    RESULTS. 

IN    VERTICALS,    THE    HOLMES- WINSTANLEY 

^      SYSTEM    (CONTINUOUS  or   INTERMITTENT)      J 
IS    SIMPLE    AND    UNIQUE. 


CORRESPONDENCE 
INVITED. 


WINSTANLEY  &  Co., 

CARBONIZING  SPECIALISTS, 

KING'S  NORTON. 


liv 


MODERN     GASWORKS     PRACTICE 


MELDRUM 


5S  FURNACES 


For  Burning  Coke  and  Breeze. 


HIGHEST     EFFICIENCY. 


LARGEST     OUTPUT     OF    STEAM. 


Over   400    Gasworks    equipped.     Over  16,000    Furnaces  Supplied. 
Suitable   for  Boilers   of  all  Types,    also    Tar    Stills. 


MELDRUM    IMPROVED    SILENT    FURNACES    ON     LANCASHIRE    BOILERS. 

We  also  make  ACID  ELEVATORS,  TAR  &  OIL  BURNERS, 
RETORT  SCURFERS,  AIR  &  GAS  COMPRESSORS, 
EXHAUSTERS,  STEAM  JET  BLOWERS  of  all  TYPES. 

Inquiries  invited  by 

MELDRUMS  LIMITED,  Timperley,  nr,  Manchester 


MODERN   GASWORKS   PRACTICE  Iv 

Naphthalene  Solvent. 

"GAZINE" 

(Registered  in  England  and  Abroad.) 

> 

A  Radical  Solvent  and  Preventative  of 
Naphthalene  Deposits,  and  for  the 
Automatic  Cleaning  of  Mains  and 
Services.  It  is  used  also  for  the 
Enrichment  of  Gas. 

SUPPLIED  ONLY  BY 

C.  BOURNE, 

West  Moor  Chemical  Works, 

KILLING  WORTH. 

OB   THROUGH   HIS   AGENTS, 

F.    J.    NICOL    &    CO., 

Pilgrim   House,  Newcastle=on=Tyne. 

TVW,        •    (  "  DoR'C,  NEWCASTLE-ON-TYNE."     National  Telephone  2497. 
lelegrams.    £  "  BOURNE,  pOREST  HALL;. 


Ivi 


MODERN   GASWORKS   PRACTICPZ 


GAS  HEATED  FURNACE 

For  Low  Pressure  Gas  and  Air  under  Pressure. 


Suitable  for  all  Industrial  purposes  such  as  Hardening,  Carbonising, 
Annealing,  Tempering,  &c. 


Any  size  made  to  order. 


FULL    PARTICULARS     FROM 


FLETCHER,  RUSSELL  &  CO,,  LTD., 

PALATINE  WORKS,  WARRINGTON. 


MODERN   GASWORKS   PRACTICE 


Ivii 


©WIR  FROM 


A  useful  help  in  selling 
gas  for  power 

~MAY    WE    SEND    TOU    COPIES  ? 


In  a  28  pp.  Booklet  entitled  "Power 
from  Town's  Gas  "  we  have  marshalled 
the  evidence  in  favour  of  gas  as  a 
motive  power,  and  demonstrate  con- 
clusively that,  used  in  conjunction 
with  CROSSLEY  GAS  ENGINES,  gas  is 
preferable  to  either  steam  or  elec- 
tricity. This  booklet  is  just  the  thing 
to  hand  to  a  client  who  is  wavering 
in  his  choice  of  power,  and  we  shall 
be  pleased  to  place  copies  at  your 
disposal. 


The  reputation  of  Crossley  Gas  Engines 
is  world  wide — over  80,000  have  been 
sold.  The  excellence  of  Crossley  design 
and  workmanship  ensures  maximum 
efficiency  under  all  conditions.  -Every 
Crossley  owner  is  a  gas  enthusiast — 
every  user  in  your  town  an  asset  to 
your  Company. 

We  are  wishful  to  co-operate  with 
every  gas  manager  to  disseminate  facts 
as  to  the  economy  of  gas  power.  Will 
you  write  us  for  full  information  ? 


Town's  Gas  Engine  Dept., 
CROSSLEY     BROS.,     LTD.,     OPENSHAW,     MANCHESTER. 

Branches  and  Agents  all  over  the  World. 


Iviii 


MODERN   GASWORKS   PRACTICE 


BABCOCK  &  WILCOX 

LIMITED. 

PATENT     WATER-TUBE    STEAM     BOILERS. 

12,4OO,OOO   H.P.   Land  Type  for  Stationary  Purposes. 
3, 8OO,OOO    H.P.    Marine  Type  Afloat. 

BABCOCK  &  WILCOX  also  supoly,  as  Joint  Manufacturers  and  General  Licensees  with  J.  SAMUEL 
WHITE  &  CO.,  LIMITED,  the  WHITE-FORSTER  BOILERS  for  DESTROYERS,  TORPEDO 

BOATS,  PINNACES,  etc. 

CONVEYORS  FOR  HANDLING  COAL  &  COKE,  Etc. 


PROVAN     GASWORKS,     GLASGOW,     SCOTLAND. 

Installation  of  Five  Babcock  &  Wilcox  Gravity  Bucket  Conveyors  for  Handling  and 

Distributing  Coke. 

BABCOCK  &  WILCOX  MANUFACTURE 
SILENT     GRAVITY    BUCKET    CONVEYORS. 
TIPPING    TRAY     CONVEYORS. 

COAL    AND     HOT    COKE    CONVEYORS. 
COAL    AND     COKE    BREAKERS. 

AUTOMATIC    RAILWAYS,    &c.,    &c. 

HEAD    OFFICE  : 

Oriel  House,  Farringdon  Street,  London,  E.G. 

Telegrams:  "BABCOCK  LONDON."        Works  :  RENFREW,  SCOTLAND.        Telephone  No.  :  City  6470  (8  lines). 


MODERN   GASWORKS   PRACTICE  lix 


LEEDS  &  BRADFORD  BOILER  CO.,  LTD., 


Contractors  to  War  Office,  India  Officp,  Admiralty,  Crown  Agents  for  the  Colonies,  etc. 

Tar  Distilling  Plants 
High-class  Tar  Stills 

The  Channel  and  Dome  Plates  are  all  pressed  at 
one  heat  by  hydraulic  pressure. 

Every  rivet  hole  in  this  bottom  is  drilled  in 
position  after  the  plates  are  pressed  into  shape. 

All  these  seams  are  rivetted  up  by  hydraulic, 
and  caulked  by  pneumatic  pressure. 

The  Run-oft  Pipe  is  made  of  wrought  mild  steel 
plates  and  solid  welded. 

NEW  STILL  BOTTOMS 

Chemical  Works  Plant,  Benzol  Stills,  Ammonia  Stills,  Phenol  Stills, 
Oil  Stills,  Washers,  Air  Receivers,  Condensing  Tanks,  Storage  Tanks, 
Jacketted  Pans,  Digesters,  All  kinds  of  Wrought  Steel  Plate  Work, 

Coils,  Piping,  etc. 


CAST=IRON    GAS 

PIPES 

1|-in.  to  12-in.  bore. 
ALSO  FOR 

WATER,   SEWAGE   AND    STEAM. 


THOMAS  ALLAN   &  SONS,  LTD., 

BON  LEA  FOUNDRY, 

THORNABY-ON-TEES. 


Ix  MODERN   GASWORKS   PRACTICE 

THOMAS  VALE  &  SONS, 

STOURPORT,    Wares.     LtcL 

Telephone:  7  Stourport.  Telephone:  "Vale,  Stourport." 

London  Office :  PALACE  CHAMBERS,  WESTMINSTER,  S. W. 

Complete  Installations  of 

Horizontal  Retorts 


(Klbnne  Regenerative  System) 


Vertical  Retorts 

(Woodall-Duckham    System) 

Gasholder  Tanks 

Brick    and    Puddle    or    Reinforced    Concrete 


FOUNDATION    WORK.  MAIN    LAYING. 

Retort   House  and   other   Buildings, 

HIGH-CLASS  WORK. 


MODERN   GASWORKS   PRACTICE 


Ixi 


"NATIONAL" 

COKE-FIRED 

STEAM  LORRY 


per  mile  for  a  3-ton  load, 


Write  for  Particulars  to  the 

NATIONAL  STEAM  CAR  CO.  Ltd. 

16,  St.   Helens  Place, 
BISHOPSGATE,    LONDON,    E.G. 

Works:   CHELMSFORD 


Ixii 


MODERN  GASWORKS   PRACTICE 


HEAVY  CAST=IRON  COCKS 

FOR  TAR,  LIQUOR,  STEAM  AND  WATER. 

Special    Heavy    Designs   for   Gasworks   Use   and  Chemical   Plant. 

Tested  to  90  IBs.  Hydraulic  Pressure  per  square   inch. 

GLAND  COCKS.     GLAND  COCKS.     PLUG  COCKS.    PLUG  COCKS. 


No.  113. 
Screwed  Ends. 


No.  114. 
Flanged  Ends. 


No.  115. 

Screwed  Ends. 


No.  116. 
Flanged  Ends. 


SULPHATE    PLANT    FITTINGS. 

Haughton's  Improved  Non-  Rotative  Acid   Valves. 


No.  119.  No.  120. 

FLANGED  BIB  VALVE.  FLANGED  STRAIGHT  VALVE. 

Regulus  Acid  Valves  for  Saturators. 

Made  of  Acid-Resisting  Metal  throughout  for  Sulphuric  Acid.     The  Finest  Acid  Valves  for  Sulphate 

of  Ammonia  Plant. 
'  PATE*T  t  I  ±  J          30     ST.    MARY-AT-HILL, 


ft  I  ±  J          30     ST.    MARY 

tO.,    Ltd.,    LONDON,  E.G. 


Telegrams  —  "  Hsughnot,  Bilgate,  London." 


Telephone     Aver.ue  5605. 


MODERN   GASWORKS   PRACTICE  Ixiii 

E.  COCKEY  &  SONS,  LTD., 

Iron   Founders,  Gas  and 
Constructional  Steel  Engineers. 

Manufacturers  of  all  descriptions 
of  Plant  for  GASWORKS,  COKE 
OVEN  INSTALLATIONS  and 
RESIDUAL  PRODUCTS  WORKS. 

NON-MECHANICAL     WASHERS 

(Cockey's  Patent) 

TOWER     SCRUBBERS 

(Cast  Iron  or  Steel) 

DEPHLEGMATORS 

PURIFIERS 

TAR  DEHYDRATION  PLANTS 

OIL  STORAGE  TANKS 

Also 

COCKEY'S       PATENT       REVER- 
SIBLE   CENTRE    VALVE 

The    only    valve    of    its    kind. 


WORKS:  LONDON      OFFICE: 

FRO  ME,     SOM.  39     VICTORIA    STREET,     S.W. 

Telegrams: -COCKEY'S,     FROME.  Telegrams  :— "  Edcosolim,"    Vic.,     London. 

Telephone  :  —16     FROME.  Telephone: — No.    5238  Victoria. 


MODERN  GASWORKS  PRACTICE 


,  HOWL  &  Co.,  Ltd. 
TIPTON 


*  —  =.  -  > 


WORKS    PUMPS 


jqu 


MODERN  GASWORKS  PRACTICE 


Books  for  Gas  Men. 


MODERN  RETORT  SETTINGS: 

Their  Construction  and  Working. 

By  T.  BROOKE. 

Demy  8vo.         202  pages,  with  158  illustrations.         Price  7s.  6*L  net. 

**  The  Journal  of  Ga»  LLfhtinf  **  says  :— "This  work  is  aa  up-to-date  account  of  retort  setting* 
as  now  used  in  modern  gasworks ;  and  it  is  not  difficult  to  see  that  the  author  write*  of  a  TifHfrt  in 
which  he  is  both  interested  and  experienced.  .  .  .  The  author's  riews  on  construction  are 
distinctly  sound." 

ESTIMATES  AND  VALUATIONS. 

A  Handbook  of  Data  and  Prices  for  Gas   Engineers. 
By  JESSE  F.  SCOTT,  Assoc.M.Inst.C.E. 

Demy  8vo.     Part  I. — Building  Works;   Part  II. — Gasworks  Plant,  etc.     With   Tables. 

Prices  10s.  6tL  net. 

The  late  SIR  CORBET  WOODALL,  J.P..  D.Sc^  M.Lm.C^.  in  an  introductory  note,  wrote  :— 
"The  author  has  been  well  known  to  me  for  upwards  of  twenty  years,  and  he  has  had  many 
opportunities — of  which  he  has  taken  full  advantage — of  making:  \n*n*rtf  *rrjn*lntfA  with  the  costs  ot 
new  Gasworks  as  well  as  the  extensions  of  those  already  existing." 

COAL  TAR  DISTILLATION 

and  Working  Up  of  Tar  Products. 

By  ARTHUR  R.  WARNES, 

Chemical  Engineer  and  Technical  Chemist ;  Mem.  Sac.  Chem.  Industry ;  Mem.  Faraday  Sac..  •**•- 

Demy  8vo.       With  Illustrations.       Price  7s.  6d.  net. 

Contents  : — Coal  Tar. — How  Tar  is  Received  from  Gasworks. — Plant  used  in  Distillation  of  Tar. — 
Distillation  of  Coal  Tar.— Plant  for  Recovering  Cresylic  and  Carbolic  Acids  from  03. — The  Recovery 
of  Carbolic  and  Cresylic  Acids. — Plant  for  th*  Recovery  of  Benzols.  Naphthas,  etc. — The  Recovery 
of  Benzols  and  Naphthas. — First  Distillation  and  Washing. — The  Rectification  of  Benzols  and 
Naphthas.— Plant  for  the  Working  up  of  Pyridene  from  Pyridene-Acid. — The  Recovery  and  Rectifi- 
cation of  Pyridene  Bases. — Plant  for  the  Manufacture  of  Crude  Naphthalene  and  Anthracrae. — 
The  Manufacture  of  Crude  Naphthalene  and  Anthracene. — Pitch  and  Pitch  "Getting."" — Creosote. — 
Tar  Works'  Tests. — Appendix. 

DISTRIBUTION    OF    GAS. 

By  WALTER   HOLE, 

Member  of  the  Institution  of  Gas  Engineers.  Superintendent  of  the  City  of  Leeds  Gas  Mains  and 
Distribution  Department.  Lecturer  on  Gas  Distribution  at  the  University  of  Leeds.  Examiner  in  Gas 
Supply  to  the  City  and  Guilds  of  London  Institute. 

Third  Edition.    Revised  and  Enlarged.    Demy  8vo.   900  pages,  with  nearly  700  Illustrations. 
Cloth,  gilt  edges.     Price  15s.  net. 

CARBONIZATION    OF    COAL. 

A  Scientific  Review  of  the  Formation,   Composition    and    Destructive    Distilla- 
tion of  Coal  for  Gas,  Coke  and  By. Products. 

By  VIVIAN    BYAM   LEWES,  F.I.C.,  F.C.S. 

Professor  of  Chemistry,  Royal  Naval  College.  Greenwich.  Chief  Superintending  Gas  Examiner  to 

the  Corporation  of  the  City  of  London.  Vice-President  of  the  Institution  of  Naval  Architects,  etc. 

Demy  8vo.     360  pages,  with  30  Illustrations.     Price  7s.  6d.  net. 

"  The  Times  "  says  :— "  Will  be  hailed  with  satisfaction  by  all  those  who  are  interested  in  carbon- 
izing work  and  who  desire  to  possess  the  most  recent  information  on  this  important  subject." 

CONSTRUCTION     AND     MANAGEMENT 
OF    SMALL    GASWORKS. 

By  NORTON    H.    HUMPHRYS,  Assoc- M.Inst.C.E.,  F.C.S. 

With  a  section  on  COSTS  AXD  CAPACITY  OF  WORKS,  by  J.  H.  BREARLEY. 

Crown  8vo.       With  Illustrations.       Price  7s.  6d.  net. 


JOHN  ALLAN  &  CO.,  "The  Gas  World"  Offices,  8,  Bouverie  Street,  London,  E.d 


Ixvi 


MODERN   GASWORKS   PRACTICE 


AMMONIA  STILLS. 

GAS    WASHERS. 

LIQUOR     AMMONIA 
PLANT. 

PLANT  FOR 
Ammonium 
Sulphate, 

Muriate, 
and 

Nitrate 


SULPHURIC 

ACID 

PLANT 

Designed, 
Erected, 
and  Worked. 


Dearsenicating  Plant. 


DAVIS     BROS., 

66  Deansgate, 

MANCHESTER, 

and  265  Strand,  London,  W.C. 


MODERN    GASWORKS    PRACTICE 


Ixvii 


Sturtevant 
Gas  Exhausting 
or  Boosting  Fan. 


T 


nstal   Sturtevant  Gas  Boosters  and 


Exhausters  for  increasing  the  pressure  in  the  mains 
and  for  sending  gas  to  distant  holders.  For  the  manu- 
facture of  Carburetted  Water  Gas,  use  Sturtevant  special 
heavy  pattern  Blowers. 

We  shall  be  pleased  to  give  you  full  -particulars. 
Send    us    your   Enquiries    mentoining    "  G-P." 


Engineering  Co.  Ltd. 

47  Queen  Victoria  Street,  London. 


Sturtevant 
Carburetted 
Water  Gas  Plant 
driven  by 
Steam  Turbine. 


Ixviii 


MODERN   GASWORKS   PRACTICE 


A  VERY 
AUTOMATIC  SCALES 


IN 


MODERN  GASWORKS  PRACTICE. 


An  installation    of    ONE  of    SIX     "AVERT' 
AUTOMATIC     HOPPER     TOTALISERS    at 
the     works     of     the    LIVERPOOL    GAS    Co. 


W. 


T.  AVERT,  Ld 

SOHO     FOUNDRY, 

BIRMINGHAM. 


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